Oestrogen-induced increase in uterine cGMP content: A true hormonal action?

The dependency of the oestrogen-induced increase in uterine cGMP content towards the cytosol-nuclear receptor system was investigated. The following observations were made: (1) With oestradiol-17 beta (E2-17 beta), U11-100A (UA) or CI-628 (CI) the cGMP response elicited in the uterus of immature rats followed a course that was parallel to (yet delayed by about 1 h from it) the known time-course evolution of nuclear occupancy by the complex formed by each compound with the oestrogen-receptor. (2) While a marked (about 2-fold) increase in uterine cGMP content was obtained with 0.1 microgram E2-17 beta, oestradiol-17 alpha (E2-17 alpha) given at the same dose had no effect on uterine cGMP. (3) The 2--3 h response to E2-17 beta (or to UA) could not be obtained in animals that had received a first injection of E2-17 beta, 2 h, or of one of the anti-oestrogens UA or tamoxifen, 20--22 h prior to the test injection of E2-17 beta. Those 3 treatments have in common that, at the time indicated, they create a state of depletion in the uterine cytosolic receptor population. The cGMP response to E2-17 beta was restored 20--22 h following a first injection of E2-17 beta. This time is known, in this case, to correspond to full replenishment of the cytosol-receptor population. In all those tests, the wet weight increase, measured in the same organs, behaves exactly as did the cGMP response. These results support the conclusion that the increase in uterine cGMP after oestrogen administration to the immature rat, represents a true hormonal action which, like other uterotrophic actions of oestrogens, involves binding of the hormone by the cytosol receptor.     

Inhibitors of protein and RNA synthesis and 1,25-dihydroxycholecalciferol formation in vitro

Formation of 1,25-dihydroxycholecalciferol (1,25 (OH)₂CC) from 25-hydroxycholecal-ciferol (25 OHCC) was studied in isolated renal tubules prepared from vitamin D-deflcient chicks. Cycloheximide and puromycin inhibited the rate of formation of 1,25 (OH)₂CC, giving an apparent initial half-life for the activity of the 25 OHCC-1-hydroxylase enzyme in this system of $\text{3}\text{1}\text{2}\text{–4}\text{h}$. 6 h pre-incubation with actinomycin D or α-amanitin did not inhibit the enzyme's activity, suggesting that the half-life of the messenger RNA responsible for the synthesis of the enzyme is considerably greater than 6 h in the chick. Neither cycloheximide nor actinomycin D prevented the stimulation of the enzyme's activity by dibutyryl cAMP, showing that this stimulation is independent of new protein synthesis.     

Specificities in the synthesis of a cytoplasmic estrogen-induced uterine protein

The earliest known induction by estrogen of a specific uterine protein is that of the ‘induced protein’ (IP) of Gorski and colleagues, which is demonstrable within 40 min after treatment. We found that this protein is not restricted to the rat; it was detected in the uterus of prepuberal C3H/eB and SWR mice, l h after injection of 4 μg of estradiol-17β. IP was also induced in vivo by the non-steroidal plant estrogens genistein (1250 μg/rat) and coumestrol (300 μg/rat) and the synthetic estrogen diethylstilbestrol (5 μg/rat). We found no significant increase in the stimulation of the rate of IP synthesis by estrogen in uteri from either 10- or 20-day-old rats on subsequent treatment with actinomycin D, indicating that there was no superinduction of IP, despite a previous claim.     

Oestrogen receptors and oestrogen-induced protein synthesis in the uterus of diabetic rats

Summary The present study was undertaken to examine whether the diabetic state influenced the early stages of oestrogen action in the uterus. Ovariectomized streptozotocin diabetic rats were given intravenous infusions of oestradiol-17 B one day to 4–7 months after the initiation of diabetes. Oestradiol was taken up to a similar extent (on a wet weight basis) by the uteri of diabetic and control animals. Oestradiol receptor levels were similar in the cytosol of control and diabetic rats (1.06±0.19 and 1.01±0.27 pmol/uterus respectively). Nuclear translocation of the receptor complex under the influence of oestradiol infusion occurred similarly in both groups. The stimulation of a specific oestrogeninduced protein in the uteri occurred at a similar rate in both groups from one day to 4–7 months after the onset of diabetes. Thus streptozotocin diabetes of short to long duration does not interfere with the early stages of oestrogen action.     

一种乙型肝炎病毒转录后调节基序的体外合成方法

目的 探索T7 RNA聚合酶体外转录方法制备乙型肝炎病毒（HBV）转录后调节基序（HPRE）。方法 用聚合酶链反应法从含HBV全基因组的模板中扩增HBV HPRE基因，重组人pGEM—11zf载体，并用T7 RNA聚合酶对其进行体外转录。结果 成功地构建含HPRE基因的重组质粒，并成功地用体外转录方法制备了高纯度的HPRE。结论 T7 RNA聚合酶体外转录方法可用于制备高纯度的HPRE，为以后的深入研究奠定了基础。     

Evidence for the involvement of lutropin-independent RNA synthesis in Leydig cell steroidogenesis.

The effect of incubating purified Leydig cells in Eagle's medium and the subsequent effect of the RNA synthesis inhibitors, actinomycin D and cordycepin, on lutropin-stimulated testosterone synthesis have been investigated. The inhibiting effect was found to be inversely related to the time of preincubation; with cells preincubated for 0, 1, 2 and 3 h with Eagle's medium only, followed by 2-h incubation with lutropin with and without actinomycin D, testosterone synthesis was inhibited by 37 +/- 4, 31 +/- 3, 18 +/- 4 and 14 +/- 3% respectively (means +/- s.e.m., n = 5). In cells that had been preincubated for 3 h there was no significant effect of actinomycin D on testosterone synthesis during the first hour of incubation with lutropin. Thereafter the inhibition increased with time reaching a maximum of 30% after 5 h. The effects of preincubation were not due to endogenous lutropin in the Leydig cells because cells isolated from hypophysectomized rats gave similar results. The inhibition of [3H]uridine incorporation into the Leydig cell RNA was 80 +/- 1% with 8 microgram/ml actinomycin D. Increasing the concentration of this inhibitor to 80 microgram/ml did not significantly increase the inhibition of [3H]uridine incorporation or lutropin-stimulated steroidogenesis in preincubated and non-preincubated cells. With cordycepin the inhibition of both RNA synthesis and lutropin-stimulated testosterone synthesis in non-preincubated cells were the same; with 25.1--251 microgram/ml approx. 30--70% resp. With preincubated cells (3 h), 0--50% inhibition of testosterone synthesis was obtained respectively. The inhibitory effect of actinomycin D oimilar to that obtained with lutropin. These observations suggest that during preincubation and independently of lutropin, synthesis of intermediates, including RNAs required for stimulation of steroidogenesis, takes place and that subsequent stimulation of steroidogenesis by lutropin occurs without further de novo RNA synthesis. These results provide evidence for a permissive role of specific RNA and protein synthesis in the action of lutropin on testosterone synthesis in the Leydig cell.     

Inhibition of protein synthesis in irradiated larvae of Schistosoma mansoni

UV-irradiated and gamma-irradiated schistosomula of Schistosoma mansoni induce high levels of resistance to challenge infection in experimental hosts. It was observed that both types of irradiation severely inhibited protein synthesis by the parasite larvae. Schistosomula were treated with the metabolic inhibitor actinomycin D to simulate this effect of irradiation. The ability of these drug-treated larvae to induce immunity was tested in animal protection experiments. Our results suggest that inhibition of protein synthesis may help to generate the enhanced immunogenicity of irradiated schistosomula. In explanation, we propose that irradiated schistosomula may be such potent immunogens because they express antigens in disrupted, abnormal conformations. Inhibition of protein synthesis may both directly create such modified antigens, and also ensure that they persist and accumulate for presentation to the host immune system.     

Storage of platelets: effects associated with high platelet content in platelet storage containers

Background

A major problem associated with platelet storage containers is that some platelet units show a dramatic fall in pH, especially above certain platelet contents. The aim of this study was a detailed investigation of the different in vitro effects occurring when the maximum storage capacity of a platelet container is exceeded as compared to normal storage.

Materials and methods

Buffy coats were combined in large-volume containers to create primary pools to be split into two equal aliquots for the preparation of platelets (450–520×10⁹ platelets/unit) in SSP+ for 7-day storage in two containers (test and reference) with different platelet storage capacity (n=8).

Results

Exceeding the maximum storage capacity of the test platelet storage container resulted in immediate negative effects on platelet metabolism and energy supply, but also delayed effects on platelet function, activation and disintegration.

Conclusion

Our study gives a very clear indication of the effects in different phases associated with exceeding the maximum storage capacity of platelet containers but throw little additional light on the mechanism initiating those negative effects. The problem appears to be complex and further studies in different media using different storage containers will be needed to understand the mechanisms involved.     

Progesterone inhibition of uterine nuclear estrogen receptor: dependence on RNA and protein synthesis.

Progesterone treatment was found previously to reduce nuclear estrogen receptor (Re) rapidly (2-4 hr) in the hamster uterus in vivo. The present study was done to determine whether this inhibitory effect of progesterone on uterine nuclear Re could be demonstrated in vitro ad whether progesterone action was dependent on RNA and protein synthesis. A uterine strip system was used in which estradiol pretretment caused cytosol Re translocation to the nucleus and increased synthesis of cytosol progesterone receptor (Rp) during a 16-hr incubation. When progesterone was added to the medium 4 hr before the end of the incubation, cytosol Rp was depleted and nuclear Re was greatly reduced. Further experiments done with actinomycin D, puromycin, and cycloheximide indicated that the progesterone-induced loss of uterine nuclear Re was dependent on RNA and protein synthesis. These results suggest that progesterone reduced nuclear Re through a mechanism involving Rp translocation and the induction of RNA and protein synthesis, a product of which is active in degrading or otherwise inactivating nuclear Re.     

蛇床子素体外抗犬源蓝氏贾第鞭毛虫作用研究

目的观察蛇床子素在体外抗犬源蓝氏贾第鞭毛虫的作用效果。方法本研究首先分析了不同浓度蛇J术子素对犬贾第虫滋养体的生长抑制作用,进而研究了在IC-50浓度下蛇床子素对贾第虫虫体活力的影响。结果生长抑制试验显示,不同浓度的蛇床子素均对贾第虫的生长有一定的抑制作用,而且随着浓度的增高,生长抑制作用越明显,尤其是在5．0mg／ml,培养48h,可使犬贾第虫数量减少78．62％;运动性检测试验显示在IC-50浓度下,蛇床子素对贾第虫活力具有明显的抑制作用。结论蛇床子素具有一定的抗贾第虫作用,这为蛇床子素在贾第虫病的防治方面的应用提供了理论基础。     

Danazol: in vitro effects on human hemopoiesis and in vivo activity in hypoplastic and myelodysplastic disorders

Abstract: We examined the effects of danazol on in vitro growth of human bone marrow and peripheral blood progenitor cells from 15 normal donors and 5 myelodysplastic patients, and on in vivo hemopoiesis in 30 patients with hypoplastic or myelodysplastic disorders. At concentrations similar to that reported as the plasma level after oral administration, danazol significantly increased CFU-GM colony growth in all normal donors, while the influence on CFU-E, BFU-E, CFU-MK and CFU-GEMM colony growth was less evident. The stimulatory effect on CFU-GM was observed even after accessory cell depletion. No stimulatory effect either in vitro on the growth of all hemopoietic progenitors or in vivo was observed in 15 myelodysplastic patients, while 7 complete and 3 partial hematological responses occurred in 15 patients with hypoplastic disorders. In conclusion, our results suggest that danazol exerts a direct stimulatory activity in vitro at least on CFU-GM, and a hemopoietic stimulatory effect in vivo in hypoplastic but not in myelodysplastic disorders.     

Phosphodiesterase inhibitors cause relaxation of the internal anal sphincter in vitro

PURPOSE: Pharmacologic treatments are gaining widespread acceptance as first-line therapy for anal fissure. However, existing treatments have limited clinical usefulness because of side effects and incomplete healing rates. METHODS: Fresh human surgical resection specimens containing internal anal sphincter and rectal circular muscle were collected. Strips of smooth muscle were cut from each muscle group and mounted in a superfusion organ bath. The effects of increasing concentrations of phosphodiesterase inhibitors were evaluated. RESULTS: All phosphodiesterase inhibitors tested caused a dose-dependent reduction in the tone of the internal anal sphincter, with potencies as follows: vinpocentine (phosphodiesterase-1 inhibitor; 50 percent maximum inhibition concentration = 0.87 ± 0.10 M), erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride (phosphodiesterase-2 inhibitor; 32 ± 4.8 M), trequinsin (phosphodiesterase-3 inhibitor; 0.28 ± 0.041 M), rolipram (phosphodiesterase-4 inhibitor; 63 ± 9 M), zaprinast (phosphodiesterase-1,5,6,9,11 inhibitor; 3 ± 0.69 M), and dipyridamole (phosphodiesterase-5,6,8,10,11 inhibitor; 5.5 ± 2 M). Although all inhibitors were also effective on rectal circular muscle strips, erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride, trequinsin, and rolipram were at least an order of magnitude more potent in this tissue than in the internal anal sphincter. CONCLUSIONS: There are several functionally important phosphodiesterases in the internal anal sphincter and rectal circular muscle. Both adenosine 3, 5-cyclic monophosphate and guanosine 3,5-cyclic monophosphate appear to be important in the myogenic tone of the internal anal sphincter, and this study provides further evidence of the sphincteric specialization of this tissue. Phosphodiesterase inhibitors might represent a new therapy for the treatment of anal fissure.     

多种体外预处理对胰岛移植物免疫原性影响的研究

胰岛移植物经２４℃培养、冷冻保存、激光照射在２４℃培养加冷冻保存等体外预处理后，其胰岛淋巴细胞混合培养（ＭＬＩＣ）的ｃｐｍ值、制备物内ＤＲ阳性细胞数及胰岛内淋巴样细胞数均比对照组明显降低，提示上述预处理可明显降低胰岛移植物的免疫原性，从而可能减少移植物排斥，延长移植物存活。     

Storage of platelets in additive solutions: a multicentre study of the in vitro effects of potassium and magnesium

BACKGROUND AND OBJECTIVES: In a preliminary study, the presence of potassium and magnesium in a modified synthetic medium (PAS-III) was found to have a significant influence on platelet metabolism (using apheresis-derived, as well as buffy-coat-derived platelets) when compared with standard PAS-III. The differences included reduced glycolysis, as evidenced by lower consumption of glucose and lower production of lactate, but also better preservation of pH and hypotonic shock response reactivity. The results suggested that storage in modified PAS-III containing 20% plasma was comparable to storage in standard PAS-III containing 30% plasma. To confirm the preliminary results and to evaluate the effects of different preparation protocols, an international multicentre study, which included 11 different sites, was conducted. MATERIALS AND METHODS: Platelets from 30 pools of approximately 20 buffy coat (BC) units each and 24 pooled apheresis platelet units were aliquoted for storage in plasma (reference) or synthetic medium using either a specific additive solution (PAS-III) containing 30% plasma or a modification of PAS-III containing 5.0 mm potassium and 1.5 mm magnesium (PAS-IIIM) and either 30% or 20% plasma. Units were stored at room temperature with agitation for 7 days during which in vitro testing was carried out for biochemical, haematological and functional parameters. RESULTS: Storage of platelets in PAS-IIIM resulted in a reduction in the rate of glycolysis and better retention of pH and hypotonic shock response reactivity. Storage in PAS-IIIM containing 20% plasma appeared to result in the retention of in vitro properties, similar to those observed during storage in standard PAS-III containing 30% plasma. CONCLUSIONS: The results of this study confirm the preliminary results. Similar results were seen with platelets prepared by BC and apheresis methods, despite differences in equipment, the preparation technique and in the final platelet contents achieved in the platelet units. Storage of platelets in PAS-IIIM should be considered to improve platelet function and allow plasma reduction to 20%.     

Storage of platelets in additive solutions: a pilot in vitro study of the effects of potassium and magnesium

BACKGROUND AND OBJECTIVES: Platelet additive solutions (PAS) have been shown to be suitable for extended platelet storage but have required the carryover of substantial (30%) amounts of plasma for success. Improving platelet quality by optimizing the composition of PAS may allow a reduction to be made in the amount of plasma carried over. Reducing the proportion of plasma carried over would facilitate some methods of viral inactivation and make available greater amounts of plasma for other needs. MATERIALS AND METHODS: Platelets from six pools of 25 buffy coat platelet units and five apheresis platelet units were aliquoted for storage in plasma, or converted to PAS units in either a specific additive solution (PAS-III), with 30% or 20% plasma, or a modification of PAS-III containing 5.0 mm potassium and 1.5 mm magnesium (PAS-IIIM), with 30% or 20% plasma. Units were stored at room temperature with agitation for 7 days with in vitro testing for biochemical, haematological and functional parameters. RESULTS: Storage of platelets in PAS-IIIM resulted in a reduced rate of glycolysis and better retention of pH, morphology score and ATP levels. Platelets initially showed less evidence of activation when stored in PAS-IIIM, with reduced P-selectin expression. Storage in PAS-IIIM with 20% (rather than the standard 30%) plasma appeared to result in the retention of in vitro properties, similarly to storage in standard PAS-III with 30% plasma. CONCLUSIONS: Storing platelets in an additive solution containing magnesium and potassium improves the functionality of the platelets, as measured by in vitro testing, and may allow a reduction of the amount of plasma required to be carried over to the final unit.     

Modeling lymphangiogenesis: Pairing in vitro and in vivo metrics

Lymphangiogenesis is the mechanism by which the lymphatic system develops and expands new vessels facilitating fluid drainage and immune cell trafficking. Models to study lymphangiogenesis are necessary for a better understanding of the underlying mechanisms and to identify or test new therapeutic agents that target lymphangiogenesis. Across the lymphatic literature, multiple models have been developed to study lymphangiogenesis in vitro and in vivo. In vitro, lymphangiogenesis can be modeled with varying complexity, from monolayers to hydrogels to explants, with common metrics for characterizing proliferation, migration, and sprouting of lymphatic endothelial cells (LECs) and vessels. In comparison, in vivo models of lymphangiogenesis often use genetically modified zebrafish and mice, with in situ mouse models in the ear, cornea, hind leg, and tail. In vivo metrics, such as activation of LECs, number of new lymphatic vessels, and sprouting, mirror those most used in vitro, with the addition of lymphatic vessel hyperplasia and drainage. The impacts of lymphangiogenesis vary by context of tissue and pathology. Therapeutic targeting of lymphangiogenesis can have paradoxical effects depending on the pathology including lymphedema, cancer, organ transplant, and inflammation. In this review, we describe and compare lymphangiogenic outcomes and metrics between in vitro and in vivo studies, specifically reviewing only those publications in which both testing formats are used. We find that in vitro studies correlate well with in vivo in wound healing and development, but not in the reproductive tract or the complex tumor microenvironment. Considerations for improving in vitro models are to increase complexity with perfusable microfluidic devices, co-cultures with tissue-specific support cells, the inclusion of fluid flow, and pairing in vitro models of differing complexities. We believe that these changes would strengthen the correlation between in vitro and in vivo outcomes, giving more insight into lymphangiogenesis in healthy and pathological states.     

BcsA and BcsB form the catalytically active core of bacterial cellulose synthase sufficient for in vitro cellulose synthesis

Cellulose is a linear extracellular polysaccharide. It is synthesized by membrane-embedded glycosyltransferases that processively polymerize UDP-activated glucose. Polymer synthesis is coupled to membrane translocation through a channel formed by the cellulose synthase. Although eukaryotic cellulose synthases function in macromolecular complexes containing several different enzyme isoforms, prokaryotic synthases associate with additional subunits to bridge the periplasm and the outer membrane. In bacteria, cellulose synthesis and translocation is catalyzed by the inner membrane-associated bacterial cellulose synthase (Bcs)A and BcsB subunits. Similar to alginate and poly-β-1,6 N-acetylglucosamine, bacterial cellulose is implicated in the formation of sessile bacterial communities, termed biofilms, and its synthesis is likewise stimulated by cyclic-di-GMP. Biochemical studies of exopolysaccharide synthesis are hampered by difficulties in purifying and reconstituting functional enzymes. We demonstrate robust in vitro cellulose synthesis reconstituted from purified BcsA and BcsB proteins from Rhodobacter sphaeroides. Although BcsA is the catalytically active subunit, the membrane-anchored BcsB subunit is essential for catalysis. The purified BcsA-B complex produces cellulose chains of a degree of polymerization in the range 200–300. Catalytic activity critically depends on the presence of the allosteric activator cyclic-di-GMP, but is independent of lipid-linked reactants. Our data reveal feedback inhibition of cellulose synthase by UDP but not by the accumulating cellulose polymer and highlight the strict substrate specificity of cellulose synthase for UDP-glucose. A truncation analysis of BcsB localizes the region required for activity of BcsA within its C-terminal membrane-associated domain. The reconstituted reaction provides a foundation for the synthesis of biofilm exopolysaccharides, as well as its activation by cyclic-di-GMP.Polysaccharides are essential biopolymers performing diverse biological functions, ranging from energy storage to osmoregulation and cell wall formation. Extracellular polysaccharides, including cellulose, chitin, and alginate, are synthesized inside the cell from nucleotide-activated sugars and are transported across the cell membrane during their synthesis. This remarkable task is performed by membrane-integrated glycosyltransferases (GTs) that couple polymer elongation with translocation (1, 2).Cellulose is a linear polymer of glucose molecules linked via β-1,4 glycosidic linkages (3, 4) and is primarily formed by vascular plants, but also by some algae, protists, and bacteria (4–6). Cellulose is synthesized by cellulose synthase (CesA), a family 2 member of GTs (7) that processively polymerizes UDP-activated glucose via an evolutionarily conserved mechanism (2). CesAs contain eight predicted transmembrane (TM) segments and at least one extended intracellular domain adopting a GT-A fold (2, 8). The intracellular GT-A domain is responsible for donor and acceptor sugar binding, as well as for catalyzing the GT reaction, and the membrane-embedded part forms a TM pore in close juxtaposition with the catalytic site, thereby allowing translocation of the nascent polysaccharide (2).Although most eukaryotic CesAs are believed to form supramolecular complexes that organize the secreted glucans into cable-like structures, i.e., the cellulose microfibrils (9), many Gram-negative bacteria synthesize cellulose as a biofilm component (10, 11). Biofilm formation is stimulated by the bacterial messenger cyclic-di-GMP (c-di-GMP) (12), which affects a diverse group of enzymes via interaction with either covalently or noncovalently attached c-di-GMP-binding domains, such as PilZ (13–15).Bacterial cellulose synthase (Bcs) is a multicomponent protein complex encoded in an operon containing at least three genes, bcsA, B, and C (16, 17). BcsA is the catalytic subunit that synthesizes cellulose and forms the TM pore across the inner membrane and BcsB is a large periplasmic protein that is anchored to the inner membrane via a single C-terminal TM helix. BcsB may guide the polymer across the periplasm toward the outer membrane via two carbohydrate-binding domains (CBDs) (2). BcsA and BcsB are fused into a single polypeptide chain in some species (18). BcsC is predicted to form a β-barrel in the outer membrane, preceded by a large periplasmic domain containing tetratricopeptide repeats likely involved in complex assembly (16). Most cellulose synthase operons also code for a periplasmic cellulase, BcsZ, whose biological function is unknown, yet it appears to enhance cellulose production in vivo (19, 20). Although most biofilm-forming bacteria likely produce amorphous cellulose that is embedded in a 3D matrix of polysaccharides, proteinaceous fibers, and nucleic acids (21), some bacteria produce cellulose microfibrils resembling those synthesized by eukaryotic cells (22). In such bacteria, CesA complexes are linearly arranged along the cell axis, and the CesA operons encode at least one additional subunit, BcsD, that might facilitate the linear organization of the synthases (18).Despite the numerous studies available on a large number of pro- and eukaryotic model systems, revealing the mechanism of cellulose synthesis and translocation has been hampered by difficulties in reconstituting functional CesAs in a purified system, either from eukaryotic or prokaryotic enzymes (23–26). To date, cellulose biosynthetic activities have only been recovered from detergent extracts of native membranes (24–26).To overcome these challenges, we reconstituted an active cellulose synthetic system in vitro from a purified Rhodobacter sphaeroides BcsA-B complex (27). The purified complex efficiently synthesizes amorphous, high-molecular-weight (HMW) cellulose on incubation with UDP-glucose (UDP-Glc) and c-di-GMP, both in a detergent-solubilized state and after reconstitution into proteoliposomes (PLs). We show that cellulose elongation occurs directly from UDP-Glc without lipid-linked intermediates, reveal that c-di-GMP activates the synthase, and demonstrate the strict substrate specificity of BcsA for UDP-Glc. Furthermore, we demonstrate that BcsB is crucial for the catalytic activity of BcsA and localize the region required for cellulose synthesis within BcsB’s C-terminal, membrane-associated domain that packs against the TM region of BcsA.