Gene conversion and reciprocal exchange in a Ty-mediated translocation in yeast

Summary A haploid yeast mutant carrying a reciprocal translocation was analyzed. Cloning and comparison of sequences involved in the translocation event in wildtype and mutant revealed that the crossover between non-homologous chromosomes has occured within Ty sequences. By DNA sequence analysis it could be demonstrated that the reciprocal recombination event is accompanied by a short segment of non-reciprocal exchange (gene conversion) in the immediate vicinity of the crossover. Analysis of the translocation mutant and revertant isolates also indicated that the regulatory effect of Ty elements on adjacent genes can be modified by discrete changes within a Ty element.     

Insertion of non-homologous DNA sequences into a regulatory gene cause a constitutive maltase synthesis in yeast

Summary Two maltase constitutive alleles MAL1-1 ^c and MAL1-2 ^c were obtained as revertants from a defective mall-1 mutant allele not promoting maltose fermentation. Classical genetical analysis showed that the mutations were linked or allelic to the MAL1 locus. Dominance relations were established by testing -glucosidase activities in diploids containing various allele combinations.The maltose regulatory genes belonging to the MAL1, MAL1-1 ^c and MAL1-2 ^c alleles were cloned. Differences in restriction sites were found between the wild type MAL1 and the derived MAL1-constitutive alleles. The MAL1 regulatory gene was located in a 1.15 kb EcoRI fragment (Rodicio and Zimmermann 1985a, b). An EcoRI fragment of this size was found in plasmids containing the MAL1 regulatory wild type allele but was absent from plasmids carrying the constitutive alleles.The genomic organization of the MAL loci in the constitutive mutants was confirmed by Southern analysis. Various fragments containing sequences of the different MAL1 alleles were used to probe genomic digests of MAL1, MAL1-1 ^c and MAL1-2 ^c strains. The results obtained support the conclusion that the constitutive mutations had arisen by a rearrangement between the original mal1-1 mutant allele and sequences with different location in the genome.Dedicated to Prof. Dr. Fritz Kaudewitz on the occasion of his 65th birthday     

Fur regulation of Staphylococcus aureus heme oxygenases is required for heme homeostasis

Heme is a cofactor that is essential for cellular respiration and for the function of many enzymes. If heme levels become too low within the cell, S. aureus switches from producing energy via respiration to producing energy by fermentation. S. aureus encodes two heme oxygenases, IsdI and IsdG, which cleave the porphyrin heme ring releasing iron for use as a nutrient source. Both isdI and isdG are only expressed under low iron conditions and are regulated by the canonical Ferric Uptake Regulator (Fur). Here we demonstrate that unregulated expression of isdI and isdG within S. aureus leads to reduced growth under low iron conditions. Additionally, the constitutive expression of these enzymes leads to decreased heme abundance in S. aureus, an increase in the fermentation product lactate, and increased resistance to gentamicin. This work demonstrates that S. aureus has developed tuning mechanisms, such as Fur regulation, to ensure that the cell has sufficient quantities of heme for efficient ATP production through aerobic respiration.     

Second-site antibiotic resistance mutations in the ribosomal region of yeast mitochondrial DNA

Summary A large proportion of the spontaneous erythromycin resistant mutants isolated from a strain carrying a previously-induced chloramphenicol resistance mutation at cap3 do not map at ery1, the locus most often associated with mitochondrial erythromycin resistance. Most of the new mutations are also nonallelic at spil, spi2, and other known antibiotic resistance loci within the 21S rRNA gene; they are allelic with each other and define the new locus, ery2. Induced second-site erythromycin resistant mutants from the cap ^r3 strain, as well as spontaneous or induced mutants from strains carrying a cap ^r 1 mutation, all tend to map at eryl. The cap ^r3 mutation is apparently necessary for the expression of erythromycin resistance resulting from a second mutation at ery2.     

Desaturation and heme elevation during COVID-19 infection: A potential prognostic factor of heme oxygenase-1

Increased heme levels, anemia, and desaturation occur during infection. We aimed to compare the levels of heme, heme oxygenase-1 (HO-1), ferritin, and bilirubin in coronavirus disease 2019 (COVID-19) patients at different saturation levels. Heme and HO-1 enzyme levels significantly increased in the low SpO₂ group, but further studies are required.     

Functional nuclear suppressor of mitochondrialoxi2 mutations in yeast

Summary A semidominant nuclear suppressor, callednam6, ofoxi2-V276 mitochondrial mutation has been isolated and characterized. The nuclear character ofnam6 was proved by its retention inrho° strains, lack of mitotic segregation in diploids and meiotic 2:2 segregation in tetrads. The specificity ofnam6 was tested on 315mit ^– mutations of four mitochondrial genes (oxi1, oxi2, oxi3, andcob-box). It suppresses clearly only three mutations in theoxi2 gene, restoring partially or completely cytochrome aa₃ formation. The results suggest a functional character of the suppression.     

Mutations and environmental factors affecting regulation of riboflavin synthesis and iron assimilation also cause oxidative stress in the yeast Pichia guilliermondii

Iron deficiency causes oversynthesis of riboflavin in several yeast species, known as flavinogenic yeasts. However, the mechanisms of such regulation are not known. We found that mutations causing riboflavin overproduction and iron hyperaccumulation (rib80, rib81 and hit1), as well as cobalt excess or iron deficiency all provoke oxidative stress in the Pichia guilliermondii yeast. Iron content in the cells, production both of riboflavin and malondialdehyde by P. guilliermondii wild type and hit1 mutant strains depend on a type of carbon source used in cultivation media. The data suggest that the regulation of riboflavin biosynthesis and iron assimilation in P. guilliermondii are linked with cellular oxidative state.     

A regulatory mutation in yeast which affects catalase T formation and metabolism of carbohydrate reserves

Summary Mutations at the GLC1 locus in Saccharomyces cerevisiae result in a major deficiency in synthesis of catalase T, but do not affect catalase A. Three independent glc1 mutations were shown to have the same pleiotropic phenotype: catalase T deficiency, defective glycogen synthesis and defective trehalose accumulation. These three deficiencies appear to be determined by a single, nuclear gene. The possibility that glc1 mutations alter a protein kinase is considered.     

肺缺血-再灌注损伤时HO-1/CO系统的变化及葛根素对其的影响

目的：探讨兔肺缺血-再灌注损伤时血红素加氧酶－1（HO-1）/一氧化碳（CO）的变化及葛根素对其的影响。方法:复制在体兔原位单肺缺血－再灌注模型，随机分：假手术对照（control）组、肺缺血－再灌注（I-R）组与肺缺血－再灌注加葛根素（puerarin）组，每组10只。各组在缺血前、缺血1h、再灌注1 h、3 h和5 h分别抽血，检测一氧化碳血红蛋白(COHb)浓度、环磷酸鸟苷(cGMP)含量。实验结束时取肺组织检测湿干重比(W/D)、 肺泡损伤率(IAR)，观察肺组织超微结构的改变、HO-1的活力、表达部位及强度。结果:血浆COHb浓度、cGMP 含量I-R组、puerarin组明显高于control组，以puerarin组为著（P<0.01）。肺组织HO-1活性，I-R组较control组明显增加，puerarin组增加更加显著（P<0.01）。I-R组、puerarin组HO-1在肺血管内皮、部分血管平滑肌、外膜层及部分气道上皮呈阳性表达，明显高于control组，尤以puerarin组最为明显（P<0.01）。W/D、IAR，I-R组明显高于control组（P<0.01），puerarin组虽较control组为高，但显著低于I-R组（P< 0.01）。I-R组有明显的肺超微结构损伤，而puerarin组损伤较轻。结论:葛根素可通过上调HO-1表达，增加HO-1活性，对缺血再灌注肺发挥明显的保护作用。     

Simultaneous induction of multiple mutations by N-methyl-N′-nitro-N-nitrosoguanidine in the yeast Saccharomyces cerevisiae

Summary Contrary to what happens in bacteria, mutations induced by nitrosoguanidine in yeast are not accompanied by an excess of mutations in nearby genes. We have investigated nitrosoguanidine mutagenesis in three regions of the yeast genome: the contiguous DNA segments HIS4A, HIS4B and HIS4C, located on chromosome III; ADE1 and CDC15 separated by about 3 map units on chromosome I; and CAN1, some 50 map units away from the centromere on chromosome V. Revertants at HIS4C never suffered mutations at HIS4A or HIS4B. Reversion at CDC15 did not affect the frequency of mutation at ADE1. No tsm mutations, leading to thermonsensitivity, were found in the immediate vicinity of the locus CAN1 after selecting for canavanine resistant mutants. However, as expected from nitrosoguanidine mutagenesis of replication points and the fixed pattern of chromosome replication, the induced tsm mutations seem not to map randomly over the yeast genome; in fact, two out of the three groups of such tsm mutations studied are located in the same chromosome arm as CAN1, indicating that these two regions are replicated at the same time as CAN1. Replication synchrony is less than perfect, since the tsm mutations of each group affect many different genes.     

独活寄生汤含药血清对退变软骨细胞细胞色素C及pro-Caspase-9、3的影响

背景：前期研究表明细胞凋亡是关节软骨细胞的中心性特征,对软骨破坏起着支配性的作用,是关节软骨退行性改变的病理因素之一。目的：观察独活寄生汤含药血清对大鼠退变软骨细胞释放细胞色素C、proCaspase-9和proCaspase-3的影响,探讨独活寄生汤治疗骨性关节炎的可能分子生物学机制。方法：建立体外退变软骨细胞模型,分别给予独活寄生汤含药血清或空白血清干预24,48 h,收集软骨细胞,Western Blot法检测干预后退变软骨细胞细胞色素C、proCaspase-9和proCaspase-3蛋白表达。结果与结论：随着干预时间的延长,在胞浆中空白血清组和含药血清组细胞色素C蛋白释放均逐渐降低,含药血清组释放较空白血清组明显减少(P < 0.05);线粒体中空白血清组和含药血清组细胞色素C蛋白外漏均逐渐降低,含药血清组外漏较空白血清组明显减少(P < 0.05)。空白血清组和含药血清组proCaspase-9、proCaspase-3蛋白量均逐渐升高,含药血清组升高更显著,且24 h组与48 h组之间差异有显著性意义(P < 0.01)。结果提示独活寄生汤可以通过减少细胞色素C的释放,减少Caspase-9、Caspase-3的前体裂解,推测能有效抑制软骨细胞凋亡。中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Impact of patient mutations on heterodimer formation and function in human galactose-1-P uridylyltransferase

Impairment of the human enzyme galactose-1-P uridylyltransferase (hGALT) results in the potentially lethal disorder, galactosemia. One of the fundamental questions with regard to this dimeric enzyme involves the possible influence of patient mutations on heterodimer formation and activity. Indeed, considering that many if not most galactosemia patients are compound heterozygotes, this is an issue of clinical as well as basic science interest. We have utilized a yeast expression system for the human enzyme to test whether each of a small number of mutations in hGALT (S135L, F171S, F171W, Q188R, N314D, and R333W) impact either heterodimer formation or function. Our results clearly demonstrate that while a majority of the alleles tested show precisely random patterns of subunit assortment, two deviate slightly but significantly from this pattern. Similarly, while some heterodimers exhibit apparent independence of subunit activity, others do not. These data not only demonstrate that common patient mutations in hGALT can influence both heterodimer formation and function in heterozygotes, they further raise the question of whether such interactions may also occur between different mutant alleles in compound heterozygotes (i.e., patients). Indeed, such influences may underlie some of the biochemical and clinical heterogeneity observed in the galactosemia patient population.     

Isolation and characterization of S. cerevisiae mutants deficient in amino acid-inducible peptide transport

Summary The transport of small peptides into the yeast Saccharomyces cerevisiae is subject to complex regulatory control. In an effort to determine the number, and to address the function, of the components involved in peptide transport and its regulation, spontaneous mutants resistant to toxic di- and tripeptides were isolated under inducing conditions. Twenty-four mutant strains were characterized in detail and fell into two phenotypic groups; one group deficient in amino acid-inducible peptide uptake, the other with a pleiotropic phenotype including a loss of peptide transport. Complementation analysis of recessive mutations in 12 of these strains defned three groups; ptr1 (nine strains), ptr2 (two strains), and ptr3 (one strain). Isolation and screening of 31 additional N-methyl-N-nitro-N-Nitrosoguanidine (MNNG)-induced, peptide transport-deficient mutants produced one ptr3 and 30 ptr2 strains: no additional complementation groups were detected. Uptake of radiolabeled dileucine was negligible in ptr1 and ptr2 strains and was reduced by 65% and 90% in the two ptr3 mutants, indicating that all strains were defective at the transport step. We conclude that the S. cerevisiae amino acid-inducible peptide transport system recognizes a broad spectrum of peptide substrates and involves at least three components. One gene, PTR3, may play an indirect or regulatory role since mutations in this gene cause a pleiotropic phenotype.     

Positive regulatory elements involved in urea amidolyase and urea uptake induction in Saccharomyces cerevisiae

Summary Urea amidolyase and the high affinity urea uptake system are induced by allophanate. durM ^– and durL ^– recessive mutations, which are easily obtained, totally prevent this induction. They are not linked to each other nor to the concerned structural genes. Despite an intensive hunt, no mutation of repressor or classical operator type has been selected. We conclude that urea amidolyase and urea uptake induction involves at least two positive elements coded for by the durM and durL genes.     

Identification and isolation of the cytochrome oxidase subunit II gene in mitochondria of the yeast Hansenula saturnus

Summary Mitochondrial DNA from the petite negative yeast Hansenula saturnus has been isolated and sized by digestion with restriction enzymes. The size of the mitochondrial genome is approximately 47 kb. The gene for subunit II of cytochrome oxidase was localized in the genome by Southern blotting using a [³²P]-labeled probe containing the subunit II gene of the yeast Saccharomyces cerevisiae. The probe hybridized to a 1.7 kb HindIII-BamHI fragment under stringent conditions (65°C), indicating a high degree of homology between the S. cerevisiae and H. saturnus mitochondrial DNA fragments. The 1.7 kb fragment from H. saturnus was cloned into pBR322 and physically mapped. The map was used to obtain the nucleotide sequence of the subunit II gene (Lawson and Deters presented in the accompanying paper).     

Mitochondrial copper metabolism in yeast: mutational analysis of Sco1p involved in the biogenesis of cytochrome c oxidase

Saccharomyces cerevisiae Sco1p is believed to be involved in the transfer of copper from the carrier Cox17p to the mitochondrial cytochrome c oxidase subunits 1 and 2. We here report on the results of a mutational analysis of Sco1p. The two cysteine residues of a potential metal-binding motif (CxxxC) are essential for protein function as shown by their substitution by alanines. Chimeras consisting of Sco1p and its homolog S. cerevisiae Sco2p restrict the specificity of Sco1p function to the N-terminal half of the protein. A candidate region for conferring specificity on Sco1p is a stretch of hydrophobic amino acids, which act as a membrane anchor. In line with this suggestion is the result that alterations of individual amino acids within this region impair Sco1p function. Received: 30 October / 10 December 1998     

肾性高血压血管重构中血红素加氧酶的作用

目的：研究血红素加氧酶（HO）在肾性高血压所致的血管重构中的作用。方法：采用两肾一夹（2K1C）肾性高血压大鼠模型，测定术后4周主动脉中膜的厚度、主动脉组织HO活性及HO-1蛋白表达水平。结果：① 2K1C肾性高血压大鼠术后2周开始出现高血压，在术后4周血压稳定升高；Hemin组术后4周未见血压升高。②术后4周2K1C组大鼠可见主动脉中膜的厚度较假手术组高27.5％（P<0.01）； Hemin组主动脉中膜的厚度较2K1C组低16.1％（P<0.01）。③术后4周2K1C组主动脉组织HO-1蛋白表达量明显高于假手术组（P<0.01）；HO酶活性高于假手术组（P<0.05）。结论：肾性高血压导致血管重构的过程中HO系统激活。诱导HO可以降低肾性高血压大鼠的血压，抑制主动脉中膜平滑肌层的增厚。