Killer toxin production in Pichia acaciae is associated with linear DNA plasmids

Summary We have identified a strain of the yeast Pichia acaciae which produces a killer toxin active against the yeast Debaryomyces tamarii. The killer phenotype was associated with the presence of two DNA plasmids, pPacl-1 (13.6 kilobase pairs) and pPacl-2 (7.3 kilobase pairs). P. acaciae strains, cured of these plasmids by irradiation with ultraviolet light, lacked killer activity and were sensitive to toxin produced by the parental strain. A partially cured strain, GS-1215, missing only the smaller plasmid, pPacl-2, also exhibited loss of both toxin activity and immunity. Exonuclease studies revealed that both plasmids were linear double-stranded DNA molecules with 5 protected ends. The P. acaciae system differs from that of the well-studied Kluyveromyces lactis killer system both in the range of susceptible strains and in the sizes of the plasmids involved. Our studies contradict previous reports that Pichia killer systems are invariably chromosomal.     

Structure of a linear plasmid of the yeast Kluyveromyces lactis; Compact organization of the killer genome

Summary Some strains of the yeast Kluyveromyces lactis contain a pair of linear DNA plasmids, k1 and k2, 8.8 and 13.8 kilobase pairs long, respectively. Simultaneous presence of the two plasmids confer a killer phenotype on the cell by producing a toxin which blocks the growth of sensitive yeast species. Previous genetic studies have suggested that the toxin protein is coded by the k1 plasmid. We have now determined the total nucleotide sequence of k1 DNA. The genome is 8,874 base pairs in length. It contains four protein-coding reading frames, three transcribed from one strand and the fourth transcribed from the complementary strand and has terminal inverted repeats of 202 base pairs. Nuclease S1 mapping confirmed this arrangement and showed that these genes are transcribed. The terminal repeats and the four genes form an extremely compact genome, with some overlapping of genes. All four genes use highly biased codons, 86% of them having A or T at the wobble position, reminiscent of yeast mitochondrial genes. Three genes share a very similar 5 leader sequence. The nature of gene products is discussed in the light of what is known of the excreted toxin protein.     

Correlation of plasmid type and disease caused by Coxiella burnetii.

The obligate intracellular bacterium Coxiella burnetii is the etiological agent of acute Q-fever and chronic endocarditis in humans and of several zoonotic infections. The DNA from a variety of these disease isolates was compared for homology to the plasmid QpH1, found in the Nine Mile strain. Three patterns of homology were found in these isolates, i.e., one pattern identical to that of QpH1, one common to several endocarditis isolates and goat abortion isolates, and one common to the remaining group of endocarditis isolates. Plasmid DNA from the endocarditis-abortion isolate group, designated QpRS, was mapped by restriction enzyme analysis and compared with QpH1. These data show that QpRS was 2 to 3 kilobase pairs larger, contained DNA not found in QpH1, but was not generated from QpH1 by a single insertional event. Isolation of plasmid DNA from the second endocarditis group of isolates was not successful and may indicate that the plasmid has integrated into the chromosome. This analysis provides the first clear evidence that differences exist between C. burnetii isolates which cause various diseases, indicating that different C. burnetii strains may have unique virulence characteristics.     

Terminal segment of Kluyveromyces lactis linear DNA plasmid pGKL2 supports autonomou sreplication of hybrid plasmids in Saccharomyces cerevisiae

Summary By use of linear DNA plasmid pGKL2 from the yeast Kluyveromyces lactis we have constructed hybrid plasmids carrying a LEU2 gene of Saccharomyces cerevisiae as a selectable marker. The replication properties of hybrid plasmids in yeasts were investigated. We demonstrated that the insertion of a LEU2 gene into pGKL2 resulted in circularization of the hybrid plasmids and pGKL2 segment supported autonomous replication of the plasmids. Moreover, the hybrid plasmids propagated autonomously, independently of the presence of the natural pGKL2 plasmid.     

Characterization and physical map of choleraphage φ149 DNA

Choleraphage φ149 DNA is a linear double-stranded molecule 69 × 10⁶ Da or 104 kilobase pairs (kbp). From restriction enzyme analysis, it has been concluded that the DNA is circularly permuted. There are at least three S1 nuclease-sensitive sites along the length of the molecule. These sites represent single-strand interruptions repairable by T4 DNA ligase. A physical map of the DNA has been constructed using the restriction endonucleases BamH1 and BglII.     

Candida albicans- and Candida stellatoidea-specific DNA fragment.

DNA was isolated from whole cells of Candida albicans and digested with MspI restriction enzyme. In addition to the expected large number of low-molecular-weight DNA pieces resulting from the digestion, multiple high-molecular-weight (greater than 3.0 kilobase pairs) fragments were generated by this enzyme, which cleaves DNA at CCGG sequences. Some of these fragments appeared highly repeated. An MspI fragment which was similar in size to one of the repeat elements (2.9 kilobase pairs) was cloned into the ClaI site of the plasmid vector pBR322 and replicated in a suitable Escherichia coli host strain. The candidal fragment was radiolabeled and used to probe Southern blots of DNA from several Candida species, various other fungi, and mouse and human cells. Only DNA from C. albicans and a strain of Candida stellatoidea was found to contain sequences of significant homology for hybridization. The cloned fragment may possibly be of use as a DNA probe for detection of the presence of C. albicans.     

A restriction endonuclease map of the chloroplast genome of pearl millet

Chloroplast DNA from pearl millet (Pennisetum americanum) was used to construct recombinant plasmids. These plasmids contained 97 kilobase pairs of unique DNA sequences. The chloroplast DNA fragments in these plasmids were mapped with the restriction endonucleases SalI, SphI, XhoI, BglI and HpaI. The technique of overlapping hybridization or chromosome walking was used to orient these DNA fragments on a restriction endonuclease map of the chloroplast genome. The size of the chloroplast DNA from pearl millet was estimated in this fashion to be 127–138 kilobase pairs. Twenty one kilobase pairs of the cloned DNA fragments were represented twice on the genome as inverted repeats. Thus, the recombinant plasmids which were isolated contained approximately 86–93% of the nucleotide sequences in the chloroplast genome of pearl millet. Previously characterized cloned chloroplast DNA sequences from other plants were used as hybridization probes to locate the genes for the large subunit of ribulose 1,5-bisphosphate carboxylase, the -coupling factor of ATPase and the 32 kilodalton polypeptide of photo system 11 on the restriction endonuclease map of the pearl millet chloroplast genome.     

Molecular cloning of the ARG7 gene of Schizosaccharomyces pombe encoding argininosuccinate lyase

Summary A gene bank of Sau3A partially restricted Schizosaccharomyces pombe DNA in YEp13 was used to transform an arg4 mutant of Saccharomyces cerevisiae. One colony was recovered which contained the YEp13 plasmid bearing a large insert complementing the argininosuccinate lyase (ASL) mutation. As shown by restriction mapping and subcloning experiments, the DNA sequence required for complementation is localized on a 2 kb BamHI-BamHI fragment. The plasmid complemented several S. cerevisiae arg4 mutants of independent origin and a S. pombe arg7 mutant lacking ASL. Low but significant ASL activities were detected in crude extracts of these transformants. No complementation of the E. coli argH mutant was observed. Southern blot hybridizations showed that the insert originates from the S. pombe genome. No cross-hybridization was found between this sequence and S. cerevisiae DNA. It can be concluded that the cloned DNA fragment bears the S. pombe ARG7 gene coding for ASL.Abbreviations ASL argininosuccinate lyase - bp base pair - kb kilobase pair     

A kalilo-like linear plasmid in Louisiana field isolates of the pseudohomothallic fungus Neurospora tetrasperma

Two Louisiana strains of Neurospora tetrasperma contain a linear plasmid (LA-kalDNA) with a restriction map identical to the Hawaiian Neurospora intermedia senescence plasmid, kalDNA, but with termini 100 nucleotide pairs shorter. One of these strains also bore a circular plasmid similar to the Hawaiian circular plasmid Hanalei-2. One species probably acquired both plasmids from the other by horizontal transfer, at a time sufficiently distant for sequence divergence to take place. Many LA-kalDNA-bearing derivative strains senesced, but this plasmid does not guarantee senescence. Furthermore, LA-kalDNA does not insert into mtDNA. One senescent strain showed no LA-kalDNA. The plasmids are effectively transmitted via the pseudohomothallic sexual cycle. Single mating-type derivatives transmit plasmids maternally.     

Homologous linear plasmids in mitochondria of three species of wheat bunt fungi,Tilletia caries,T. laevis and T. controversa

Summary All isolates of Tilletia spp. investigated (five isolates of T. caries, including one from Japan, two isolates of T. laevis, and five isolates of T. controversa) contained a linear DNA plasmid ranging in size from 7.2 to 7.6 kb. All plasmids were highly homologous to each other as shown by DNA-DNA hybridization and comparison of restriction enzyme sites. Variability in the size of the plasmid was found to be due to differences within a central region of the plasmid. No homology between the plasmid and mitochondrial or nuclear DNA was found, but the mitochondrial origin of the plasmid was confirmed.     

Anatomy of amplified mitochondrial DNA in “Ragged” mutants of Aspergillus amstelodami: Excision points within protein genes and a common 215 bp segment containing a possible origin of replication

Summary The extranuclearly-inherited ragged growth phenotype (Rgd) of Aspergillus amstelodami is always accompanied by excision and head-to-tail amplification of mtDNA sequences. In one mutant strain (Rgd1) the amplified mtDNA segment (rgd1 DNA, monomeric length 0.9 kb) maps downstream of the large subunit ribosomal RNA gene (Region 1), whereas in all other strains analyzed the amplified sequences (rdg3-7DNA) are located in Region 2 between genes coding for cytochrome b and ATPase subunit 6. The various region 2 sequences differ in lengths (1.5 to 2.7 kb) but have in common a 215 bp sequence mapping between an. unidentified protein gene (corresponding to URF4 of human mtDNA) and an arginine tRNA gene. This common sequence may contain an origin of replication, because a looped-out hairpin structure similar to that of yeast and human mitochondrial origin sequences can be formed. Furthermore, Region 2 DNA suppresses replication of Region 1 DNA, indicating that the former group of molecules contains the more efficient origin. The nucleotide sequence of the rgd6 repeat unit starts and ends within protein genes of mtDNA, and no homologies were found between heads and tails or their flanking sequences.Abbreviations mtDNA DNA isolated from DNase — treated mitochondria - Rgd ragged mutant strain - rgdDNA highly-reiterated DNA sequences isolated simultaneously with the wild-type genome from mitochondria of ragged mutants - bp base pairs - kb kilobase pairs - URF unassigned reading frame     

Characterization of a prolate-headed bacteriophage ofLactobacillus delbrueckii subsp.lactis,and its DNA homology with isometric-headed phages

Summary A newLactobacillus delbrueckii subsp.lactis bacteriophage, JCL 1032, was characterized. JCL 1032 had a small, elongated prolate head, and a long non-contractile tail with cross-bars. The restriction map of JCL 1032 genome was constructed with five endonucleases. The genome was 45.8 kb in size, and it had cohesive ends (cos). Molecular masses of the phage structural proteins were also determined. JCL 1032 showed DNA homology with morphologically dissimilar, isometric-headed phages ofLb. delbrueckii (subsp.lactis and subsp.bulgaricus) when analyzed by Southern hybridization. Although in general JCL 1032 was only distantly related to isometric-headed phages, there were also a few short highly homologous (minimal homology 84%) DNA regions.     

Analysis of a kanamycin resistance gene (kmr) from Streptomyces kanamyceticus and a mutant with increased aminoglycoside resistance

Kanamycin resistance gene (kmr) from the overproducing mutant strain of Streptomyces kanamyceticus ISP1375 (strain 1) and from its gentamicin-resistant mutant were cloned into the high copy number vector pIJ702 and transformed into S. lividans 66. This gene provides resistance to kanamycin, gentamicin, sisomicin and tobramicin. The resistance of the transformed recipient strains was higher than the resistance level of the donor S. kanamyceticus 1. Sequencing of the kmr gene (EMBL Nucleotide Sequence Database accession no. Y15838) revealed 53.9% identity in 274 aa with the kgmB gene product (16S rRNA methylase) of S. tenebrarius. Hybridisation analysis using a 0.85 kb fragment carrying the kmr gene revealed that other gentamicin-resistant mutants of S. kanamyceticus 1 and unstable kanamycin-nonproducing mutant had a high level of kmr amplification. We found no homology between the kmr gene and the total DNA of the neomycin producer S. fradiae IFO3718; the sisomicin producer M. zionensis IFO14116 and the gentamicin producer M. purpurea ATCC15835.     

Plastid inheritance in Epilobium

Summary Interspecific hybrids of various Epilobium species have been produced in order to analyse plastid inheritance using restriction fragment polymorphisms of plastid DNA as markers. This analysis reveals that interspecific hybrids exhibit only the fragment pattern of the maternal plastome. Southern hybridization experiments using cloned species-specific plastid DNA fragments as markers confirm the maternal type of plastid inheritance in Epilobium, while providing at least a tenfold increase of sensitivity to detect restriction polymorphisms. Within the limit of detection even young seedlings contain no plastid DNA from the paternal parent. However, investigations of plastomes of large populations have provided evidence that a very low frequency of paternal plastid transmission can occur. Thus, the mechanism which ensures the elimination of paternal plastids is not 100% efficient. This suggestion is also supported by intraspecific reciprocal crosses between plants carrying mutant white and normal green plastids. While the offspring usually exhibit the maternal plastid type, a few cases indicate an apparent paternal plastid transmission.Abbreviations kbp kilobase pairs - ptDNA plastid DNA     

Physical mapping of the Borrelia miyamotoi HT31 chromosome in comparison with that of Borrelia turicatae, an etiological agent of tick-borne relapsing fever.

We report the construction of physical maps of chromosomes for Borrelia miyamotoi HT31 (a new species of Borrelia) and Borrelia turicatae (relapsing fever agent) by pulsed-field gel electrophoresis of DNA fragments generated by digestion of chromosomal DNA with rare-cutting restriction endonucleases and reciprocal hybridization. The size of the B. miyamotoi HT31 chromosome was calculated to be approximately 925 kilobase pairs, and the chromosome for B. turicatae was estimated to be 951 kilobase pairs. The chromosomes of B. miyamotoi HT31 and B. turicatae consisted of single linear molecules. The locations of several genes have been assigned to the chromosome maps by Southern hybridization by using specific gene probes. Comparison of the genetic maps of the two species of Borrelia provided evidence that the gene order on the chromosomes is quite similar to that of Borrelia burgdorferi sensu lato strains and is highly conserved in the genus Borrelia.     

Kluyveromyces lactis killer system: ORF1 of pGKL2 has no function in immunity expression and is dispensable for killer plasmid replication and maintenance

Summary To functionally characterize the genes encoded by the larger killer plasmid pGKL2 from Kluyveromyces lactis a previously developed in-vivo recombination system was exploited. An in-vitro modified version of the cytoplasmically expressible LEU2 gene cartridge (LEU2 ^*) flanked by appropriate pGKL2 segments was used to replace the central part of the ORF1 region of pGKL2. Transformation of a Leu^- killer strain resulted in the expected disruption of ORF1 in the resident pGKL2. The Leu⁺ transformants obtained can be assigned to three classes. Class I carries both killer plasmids, pGKL1/2, and the recombinant pGKL2 derivative termed pRKL2. Class II and III additionally harbor palindrome and hairpin-like plasmids, respectively. Upon subculturing of class I transformants under selective pressure, segregation of the native pGKL2 and the recombinant pRKL2 eventually occurs resulting in total loss of pGKL2. No differences concerning killer and immunity phenotype between a pRKL2-harboring strain and the native pGKL2-carrying recipient could be detected. Thus pGKL2 ORF1 is dispensable for both expression of killer/immunity phenotypes and for the replication and maintenance of the K. lactis killer plasmids.     

Encapsulation of cells in agarose beads for use in the construction of human DNA libraries as yeast artificial chromosomes (YAC)

A simple and general method for the molecular cloning of fragments of over one hundred kilobase pairs of exogenous DNA, by the encapsulation of cells in agarose beads, was developed for the construction of a human genomic DNA library in a yeast artificial YAC chromosome vector (in situ YAC construction). The main advantages of this method for use in the construction of a human genome library are as follows. First, linear DNA molecules of up to several hundred kilobase pairs in size can easily be prepared by the partial restriction enzyme digestion of the DNA encapsulated in agarose beads in vitro. Second, less than 2 x 10(6) cells scraped from tissue culture plates are sufficient for preparation of the linear DNA molecule for construction of the genome library. The technical manipulations involved in construction of clones of very large segments of DNA, including encapsulation of cells in agarose beads, restriction enzyme digestion, ligation with the YAC vector, transformation into host yeast cells, and stable propagation are discussed.     

Linear extrachromosomal DNA in the morel Morchella conica

Summary Altogether 18 different strains of the genus Morchella were assayed for the presence of extrachromosomal genetic elements. It was shown that 8 out of 13 strains of the Morchella conica group contain plasmids of comparable size (6 kb and 8 kb respectively). The 5 representatives of Morchella esculenta were not found to contain extrachromosomal DNA. The plasmid of one strain (nr. 3) was further analysed. By restriction analyses and electron microscopy it was confirmed that the plasmid is linear having a molecular weight of 6 kb. It was further shown that it carries at both ends inverted repeats of 0.75 kb.     

Cryptic DNA plasmids of the heterothallic yeast Saccharomycopsis crataegensis

Summary Three DNA plasmids, designated pScrl-1, pScrl-2, and pScrl-3 have been found in a strain of the heterothallic yeast Saccharomycopsis crataegensis (NRRL Y-5902). pScrl-l, -2 and -3 are, respectively, 15, 7, and 5 kilobase pairs (kbp) in size. Based on the results of exonuclease digestions, all three plasmids appear to be linear molecules with blocked 5 ends. All three plasmids also have a lower buoyant density than does nuclear DNA of S. crataegensis. The two lower molecular weight plasmids hybridize strongly with one another, but only weakly to the higher molecular weight plasmid. Two of four related S. crataegensis strains surveyed were found to contain two plasmids that are of the same size as the two larger plasmids of Y-5902. Evidence is presented indicating that the plasmids in strain Y-5902 reside in the cytosol since they were found not to be located within the major organelles (mitochondria and nuclei).