1
|
Fernet C, Claisse M, Clark-Walker GD. The mitochondrial genome of Debaryomyces (Schwanniomyces) occidentalis encodes subunits of NADH dehydrogenase complex I. Mitochondrion 2005; 2:267-75. [PMID: 16120327 DOI: 10.1016/s1567-7249(03)00006-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2002] [Revised: 12/04/2002] [Accepted: 12/16/2002] [Indexed: 11/15/2022]
Abstract
nad genes encoding subunits of the NADH dehydrogenase complex 1 have been revealed in the yeast Debaryomyces (Schwanniomyces) occidentalis. nad1, nad3, nad5, nad6 and most large mitochondrial genes have been located on a circular 41-kb map of mitochondrial DNA from this petite negative species. The genes nad1-nad6 are co-transcribed and the transcription is not inhibited by glucose. Sequences of nad6 and 5'-nad1 compared to homologs in other yeasts indicate better amino acids conservation for nad1 product than for nad6. A cytochrome b deficient mutant dependent on alternative oxidase and functional complex 1 for growth on respirable substrates also exhibits co-transcription of nad1-nad6.
Collapse
Affiliation(s)
- Caroline Fernet
- Centre de Génétique Moléculaire, UPR 2167 du CNRS associée a l'UPMC, Paris 6, Gif-sur-Yvette, 91198, France.
| | | | | |
Collapse
|
2
|
Clark-Walker GD, Chen XJ. Dual mutations reveal interactions between components of oxidative phosphorylation in Kluyveromyces lactis. Genetics 2001; 159:929-38. [PMID: 11729142 PMCID: PMC1461865 DOI: 10.1093/genetics/159.3.929] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Loss of mtDNA or mitochondrial protein synthesis cannot be tolerated by wild-type Kluyveromyces lactis. The mitochondrial function responsible for rho(0)-lethality has been identified by disruption of nuclear genes encoding electron transport and F(0)-ATP synthase components of oxidative phosphorylation. Sporulation of diploid strains heterozygous for disruptions in genes for the two components of oxidative phosphorylation results in the formation of nonviable spores inferred to contain both disruptions. Lethality of spores is thought to result from absence of a transmembrane potential, Delta Psi, across the mitochondrial inner membrane due to lack of proton pumping by the electron transport chain or reversal of F(1)F(0)-ATP synthase. Synergistic lethality, caused by disruption of nuclear genes, or rho(0)-lethality can be suppressed by the atp2.1 mutation in the beta-subunit of F(1)-ATPase. Suppression is viewed as occurring by an increased hydrolysis of ATP by mutant F(1), allowing sufficient electrogenic exchange by the translocase of ADP in the matrix for ATP in the cytosol to maintain Delta Psi. In addition, lethality of haploid strains with a disruption of AAC encoding the ADP/ATP translocase can be suppressed by atp2.1. In this case suppression is considered to occur by mutant F(1) acting in the forward direction to partially uncouple ATP production, thereby stimulating respiration and relieving detrimental hyperpolarization of the inner membrane. Participation of the ADP/ATP translocase in suppression of rho(0)-lethality is supported by the observation that disruption of AAC abolishes suppressor activity of atp2.1.
Collapse
Affiliation(s)
- G D Clark-Walker
- Molecular Genetics and Evolution Group, Research School of Biological Sciences, The Australian National University, Canberra, ACT, 2601, Australia.
| | | |
Collapse
|
3
|
Møller K, Olsson L, Piskur J. Ability for anaerobic growth is not sufficient for development of the petite phenotype in Saccharomyces kluyveri. J Bacteriol 2001; 183:2485-9. [PMID: 11274107 PMCID: PMC95164 DOI: 10.1128/jb.183.8.2485-2489.2001] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Saccharomyces cerevisiae is a petite-phenotype-positive ("petite-positive") yeast, which can successfully grow in the absence of oxygen. On the other hand, Kluyveromyces lactis as well as many other yeasts are petite negative and cannot grow anaerobically. In this paper, we show that Saccharomyces kluyveri can grow under anaerobic conditions, but while it can generate respiration-deficient mutants, it cannot generate true petite mutants. From a phylogenetic point of view, S. kluyveri is apparently more closely related to S. cerevisiae than to K. lactis. These observations suggest that the progenitor of the modern Saccharomyces and Kluyveromyces yeasts, as well as other related genera, was a petite-negative and aerobic yeast. Upon separation of the K. lactis and S. kluyveri-S. cerevisiae lineages, the latter developed the ability to grow anaerobically. However, while the S. kluyveri lineage has remained petite negative, the lineage leading to the modern Saccharomyces sensu stricto and sensu lato yeasts has developed the petite-positive characteristic.
Collapse
Affiliation(s)
- K Møller
- Department of Microbiology, and Department of Biotechnology, Technical University of Denmark, Lyngby, Denmark
| | | | | |
Collapse
|
4
|
Chen XJ, Clark-Walker GD. The petite mutation in yeasts: 50 years on. INTERNATIONAL REVIEW OF CYTOLOGY 1999; 194:197-238. [PMID: 10494627 DOI: 10.1016/s0074-7696(08)62397-9] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Fifty years ago it was reported that baker's yeast, Saccharomyces cerevisiae, can form "petite colonie" mutants when treated with the DNA-targeting drug acriflavin. To mark the jubilee of studies on cytoplasmic inheritance, a review of the early work will be presented together with some observations on current developments. The primary emphasis is to address the questions of how loss of mtDNA leads to lethality (rho 0-lethality) in petite-negative yeasts and how S. cerevisiae tolerates elimination of mtDNA. Recent investigation have revealed that rho 0-lethality can be suppressed by specific mutations in the alpha, beta, and gamma subunits of the mitochondrial F1-ATPase of the petite-negative yeast Kluyveromyces lactis and by the nuclear ptp alleles in Schizosaccharomyces pombe. In contrast, inactivation of genes coding for F1-ATPase alpha and beta subunits and disruption of AAC2, PGS1/PEL1, and YME1 genes in S. cerevisiae convert this petite-positive yeast into a petite-negative form. Studies on nuclear genes affecting dependence on mtDNA have provided important insight into the functions provided by the mitochondrial genome and the maintenance of structural and functional integrity of the mitochondrial inner membrane.
Collapse
Affiliation(s)
- X J Chen
- Molecular and Cellular Genetics Group, Research School of Biological Sciences, Australian National University, ACT, Australia
| | | |
Collapse
|
5
|
Abstract
Both sexual and asexual fungi undergo chromosomal rearrangements, which are the main cause of karyotype variability among the populations. Different recombination processes can produce chromosomal reorganizations, both during mitosis and meiosis, but other mechanisms operate to limit the extent of the rearrangements; some of these mechanisms, such as the RIP (repeat-induced point mutations) of Neurospora crassa, have been well established for sexual fungi. In laboratory strains, treatments such as mutation and transformation enhance the appearance of chromosomal rearrangements. Different DNA sequences present in fungal genomes are able to promote these reorganizations; some of these sequences are involved in well-regulated processes (e.g., site-specific recombination) but most of them act simply as substrates for recombination events leading to DNA rearrangements. In Penicillium chrysogenum we have found that short specific DNA sequences are involved in tandem reiterations leading to amplification of the cluster of the penicillin biosynthesis genes. In some cases, specific chromosomal rearrangements have been associated with particular phenotypes (as occurs in adaptive-like mutants of Candida albicans and Candida stellatoidea), and they may play a role in genetic variability for environmental adaptation.
Collapse
Affiliation(s)
- F Fierro
- Faculty of Biology, University of León, Spain
| | | |
Collapse
|
6
|
|
7
|
Clark-Walker GD, Chen XJ. A vital function for mitochondrial DNA in the petite-negative yeast Kluyveromyces lactis. MOLECULAR & GENERAL GENETICS : MGG 1996; 252:746-50. [PMID: 8917319 DOI: 10.1007/bf02173982] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Petite-negative yeasts do not form viable respiratory-deficient mutants on treatment with DNA-targeting drugs that readily eliminate the mitochondrial DNA (mtDNA) from petite-positive yeasts. However, in the petite-negative yeast Kluyveromyces lactis, specific mutations in the nuclear genes MG12 and MG15 encoding the alpha- and gamma-subunits of the mitochondrial F1-ATPase, allow mtDNA to be lost. In this study we show that wild-type K. lactis does not survive in the absence of its mitochondrial genome and that the function of mgi mutations is to suppress lethality caused by loss of mtDNA. Firstly, we find that loss of a multicopy plasmid bearing a mgi allele readily occurs from a wild-type strain with functional mtDNA but is not tolerated in the absence of mtDNA. Secondly, we cloned the K. lactis homologue of the Saccharomyces cerevisiae mitochondrial genome maintenance gene MGM101, and disrupted one of the two copies in a diploid. Following sporulation, we find that segregants containing the disrupted gene form minicolonies containing 6-8000 inviable cells. By contrast, disruption of MGM101 is not lethal in a haploid mgi strain with a specific mutation in a subunit of the mitochondrial F1-ATPase. These observations suggest that mtDNA in K. lactis encodes a vital function which may reside in one of the three mitochondrially encoded subunits of Fo.
Collapse
Affiliation(s)
- G D Clark-Walker
- Molecular and Population Genetics Group, Research School of Biological Sciences, Australian National University, Canberra City, Australia
| | | |
Collapse
|
8
|
Zonneveld BJ, van der Zanden AL. The red ade mutants of Kluyveromyces lactis and their classification by complementation with cloned ADE1 or ADE2 genes from Saccharomyces cerevisiae. Yeast 1995; 11:823-7. [PMID: 7483846 DOI: 10.1002/yea.320110904] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Seventy-six red adenine mutants of Kluyveromyces lactis were isolated. By complementation they could be assigned to two groups with 31 and 45 mutants. Transformation of several strains from each group with plasmids containing the Saccharomyces cerevisiae ADE1 or ADE2 gene showed that the largest group was ade2 and the other group was ade1. Several previously isolated 'ade1' mutants were classified to either group and given new gene and allele numbers. ADE1 was localized at chromosome III, closely linked to the mating type gene, making it a convenient marker for mating type. ADE2 was localized at chromosome V.
Collapse
Affiliation(s)
- B J Zonneveld
- Leiden University, Clusius Laboratory, The Netherlands
| | | |
Collapse
|
9
|
Abstract
A Kluyveromyces lactis mutant, hypersensitive to the DNA-targeting drugs ethidium bromide (EtBr), berenil, and HOE15030, can be complemented by a wild-type gene with homology to SIR2 of Saccharomyces cerevisiae (ScSIR2). The deduced amino acid sequence of the K. lactis Sir2 protein has 53% identity with ScSir2 protein but is 108 residues longer. K. lactis sir2 mutants show decreased mating efficiency, deficiency in sporulation, an increase in recombination at the ribosomal DNA locus, and EtBr-induced death. Some functional equivalence between the Sir2 proteins of K. lactis and S. cerevisiae has been demonstrated by introduction of ScSIR2 into a sir2 mutant of K. lactis. Expression of ScSIR2 on a multicopy plasmid restores resistance to EtBr and complements sporulation deficiency. Similarly, mating efficiency of a sir2 mutant of S. cerevisiae is partially restored by K. lactis SIR2 on a multicopy plasmid. Although these observations suggest that there has been some conservation of Sir2 protein function, a striking difference is that sir2 mutants of S. cerevisiae, unlike their K. lactis counterparts, are not hypersensitive to DNA-targeting drugs.
Collapse
|
10
|
Chen XJ, Clark-Walker GD. sir2 mutants of Kluyveromyces lactis are hypersensitive to DNA-targeting drugs. Mol Cell Biol 1994; 14:4501-8. [PMID: 8007956 PMCID: PMC358822 DOI: 10.1128/mcb.14.7.4501-4508.1994] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
A Kluyveromyces lactis mutant, hypersensitive to the DNA-targeting drugs ethidium bromide (EtBr), berenil, and HOE15030, can be complemented by a wild-type gene with homology to SIR2 of Saccharomyces cerevisiae (ScSIR2). The deduced amino acid sequence of the K. lactis Sir2 protein has 53% identity with ScSir2 protein but is 108 residues longer. K. lactis sir2 mutants show decreased mating efficiency, deficiency in sporulation, an increase in recombination at the ribosomal DNA locus, and EtBr-induced death. Some functional equivalence between the Sir2 proteins of K. lactis and S. cerevisiae has been demonstrated by introduction of ScSIR2 into a sir2 mutant of K. lactis. Expression of ScSIR2 on a multicopy plasmid restores resistance to EtBr and complements sporulation deficiency. Similarly, mating efficiency of a sir2 mutant of S. cerevisiae is partially restored by K. lactis SIR2 on a multicopy plasmid. Although these observations suggest that there has been some conservation of Sir2 protein function, a striking difference is that sir2 mutants of S. cerevisiae, unlike their K. lactis counterparts, are not hypersensitive to DNA-targeting drugs.
Collapse
Affiliation(s)
- X J Chen
- Molecular and Population Genetics Group, Research School of Biological Sciences, Australian National University, Canberra
| | | |
Collapse
|
11
|
Abstract
Mitochondria were isolated from the dimorphic zygomycete Mucor racemosus by differential centrifugation. DNA from the organelles was purified by cesium chloride-ethidium bromide isopycnic centrifugation. Examination of the mitochondrial DNA by electron microscopy revealed a circular chromosome approximately 63.8 kbp in circumference. The chromosome was digested with restriction endonucleases and the resulting DNA fragments were separated by agarose-gel electrophoresis. Electophoretic mobilities and stoichiometry of the fragments indicated a mixed population of mtDNA molecules each with a size of about 63.4 kbp. Physical maps were constructed from analyses of fragments generated in single and double restriction digests and from the hybridization of fragments to probes for the large and small mitochondrial rRNA genes from Saccharomyces cerevisiae. The Mucor mitochondrial chromosome was found to exist in the form of two flip-flop isomers with inverted repeat sequences encoding both rRNA genes.
Collapse
Affiliation(s)
- M L Schramke
- Department of Microbiology, Louisiana State University, Baton Rouge 70803
| | | |
Collapse
|
12
|
Clark-Walker GD. Evolution of mitochondrial genomes in fungi. INTERNATIONAL REVIEW OF CYTOLOGY 1992; 141:89-127. [PMID: 1452434 DOI: 10.1016/s0074-7696(08)62064-1] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- G D Clark-Walker
- Molecular and Population Genetics Group, Research School of Biological Sciences, Australian National University, Canberra City
| |
Collapse
|
13
|
Clark-Walker GD. Contrasting mutation rates in mitochondrial and nuclear genes of yeasts versus mammals. Curr Genet 1991; 20:195-8. [PMID: 1657417 DOI: 10.1007/bf00326232] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Base substitutions have been compared in two mitochondrial and two nuclear genes from three yeasts and three mammals. In yeasts, the two mitochondrial genes, cytochrome oxidase subunit 2 (COX2) and apocytochrome b (CYB), have fewer changes on a percentage basis than the nuclear-encoded cytochrome c (CYC) gene. By contrast, in mammals, the same mitochondrial genes have more mutations than CYC on a percentage basis. Sequence comparisons of the nuclear small-subunit ribosomal RNA (nSSU) gene shows that there are more substitutions per unit length in the three yeasts than in the three mammals. This result suggests that although the yeasts are more distantly related than the mammals, their mitochondrial genes have accumulated fewer changes.
Collapse
Affiliation(s)
- G D Clark-Walker
- Research School of Biological Sciences, Australian National University, Canberra, A.C.T
| |
Collapse
|
14
|
Skelly PJ, Hardy CM, Clark-Walker GD. A mobile group II intron of a naturally occurring rearranged mitochondrial genome in Kluyveromyces lactis. Curr Genet 1991; 20:115-20. [PMID: 1657410 DOI: 10.1007/bf00312773] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Mitochondrial intron content is variable in the yeast Kluyveromyces lactis. Strains can be divided into three classes depending on the structure of the cytochrome oxidase subunit 1 (COX1) gene: (1) those containing intron K1 cox1.1, (2) those containing K1 cox1.2, 3 and 4 and, (3) those that contain all four introns. In addition, strains belonging to the first class (designated Type B strains), have an altered mitochondrial gene order relative to strains from classes (2) and (3) (Type A, Hardy et al. 1989). Crossing experiments reveal that K1 cox1.1 (a group II intron) transfers at high frequency (89%) to mitochondrial genomes lacking this intron. By contrast, the mobility of the remaining introns (all group I) is of the order of 7%.
Collapse
Affiliation(s)
- P J Skelly
- Molecular and Population Genetics Group, Research School of Biological Sciences, Australian National University, Canberra
| | | | | |
Collapse
|
15
|
Hardy CM, Clark-Walker GD. Nucleotide sequence of the COX1 gene in Kluyveromyces lactis mitochondrial DNA: evidence for recent horizontal transfer of a group II intron. Curr Genet 1991; 20:99-114. [PMID: 1657415 DOI: 10.1007/bf00312772] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The cytochrome oxidase subunit 1 gene (COX1) in K. lactis K8 mtDNA spans 8,826 bp and contains five exons (termed E1-E5) totalling 1,602 bp that show 88% nucleotide base matching and 91% amino acid homology to the equivalent gene in S. cerevisiae. The four introns (termed K1 cox1.1-1.4) contain open reading frames encoding proteins of 786, 333, 319 and 395 amino acids respectively that potentially encode maturase enzymes. The first intron belongs to group II whereas the remaining three are group I type B. Introns K1 cox1.1, 1.3, and 1.4 are found at identical locations to introns Sc cox1.2, 1.5 a, and 1.5 b respectively from S. cerevisiae. Horizontal transfer of an intron between recent progenitors of K. lactis and S. cerevisiae is suggested by the observation that K1 cox1.1 and Sc cox1.2 show 96% base matching. Sequence comparisons between K1 cox1.3/Sc cox1.5 a and K1 cox1.4/Sc cox1.5 b suggest that these introns are likely to have been present in the ancestral COX1 gene of these yeasts. Intron K1 cox1.2 is not found in S. cerevisiae and appears at an unique location in K. lactis. A feature of the DNA sequences of the group I introns K1 cox1.2, 1.3, and 1.4 is the presence of 11 GC-rich clusters inserted into both coding and noncoding regions. Immediately downstream of the COX1 gene is the ATPase subunit 8 gene (A8) that shows 82.6% base matching to its counterpart in S. cerevisiae mtDNA.
Collapse
Affiliation(s)
- C M Hardy
- Molecular and Population Genetics Group, Research School of Biological Sciences, Australian National University, Canberra
| | | |
Collapse
|
16
|
Hardy CM, Clark-Walker GD. Nucleotide sequence of the cytochrome oxidase subunit 2 and val-tRNA genes and surrounding sequences from Kluyveromyces lactis K8 mitochondrial DNA. Yeast 1990; 6:403-10. [PMID: 2171241 DOI: 10.1002/yea.320060505] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The nucleotide sequence of the cytochrome oxidase subunit 2 (cox2) and val-tRNA genes and surrounding regions from Kluyveromyces lactis mitochondrial DNA is reported. Analysis of the coding region shows that the codons CUN (Thr), CGN (Arg) and AUA (Met) are absent in this gene. A single sequence, ATATAAGTAA, identical to the baker's yeast mtRNA polymerase recognition site, was detected upstream of val-tRNA. This sequence is absent from regions between val-tRNA-cox2 and cox2-cox1. In addition a sequence AATAATATTCTT, identical to the mRNA processing site in other yeast mitochondrial genomes is present 32-43 bp downstream to the TAA stop codon for the cox2 gene. Another short conserved sequence of 5 bp, TCTAA, is present upstream of the coding regions of cox2 genes in several yeasts, including K. lactis, but is not present upstream of other genes. Comparison of cox2 sequences from other organisms indicates that the mitochondrial DNA of K. lactis is closely related to that of Saccharomyces cerevisiae.
Collapse
Affiliation(s)
- C M Hardy
- Molecular and Population Genetics Group, Research School of Biological Sciences, Australian National University, Canberra, A.C.T
| | | |
Collapse
|
17
|
Silliker ME, Cummings DJ. A mitochondrial DNA rearrangement and three new mitochondrial plasmids from long-lived strains of Podospora anserina. Plasmid 1990; 24:37-44. [PMID: 2270228 DOI: 10.1016/0147-619x(90)90023-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The excision-junction sites of a mtDNA rearrangement of a long-lived strain of Podospora anserina, Mn19, were cloned and sequenced. Analysis of sequence and hybridization data lead to the conclusion that the Mn19 mtDNA consists of two nonoverlapping circular molecules. Three plasmids, LMt-2, LMt-3, and LMt-4, cloned from long-lived progeny of crosses between the Mn19 strain and wild type were cloned and sequenced. These plasmids share features and excision-junction sites with previously described longevity and senescence plasmids. The Mn19 mtDNA rearrangement and plasmids LMt-2, LMt-3, and LMt-4 are described. The possible significance of similarities to previously described plasmids is discussed.
Collapse
Affiliation(s)
- M E Silliker
- Department of Microbiology and Immunology, University of Colorado School of Medicine, Denver 80262
| | | |
Collapse
|
18
|
Maleszka R, Clark-Walker GD. A petite positive strain of Kluyveromyces lactis has a 300 kb deletion in the rDNA cluster. Curr Genet 1989; 16:429-32. [PMID: 2611914 DOI: 10.1007/bf00340722] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
By employing Pulsed Field Gel Electrophoresis we have shown that the chromosomal DNA pattern of a petite-positive strain of Kluyveromyces lactis, designated KF4, differs from the karyotype of the reference strain. Digestion with SfiI and hybridization with an rDNA probe, demonstrate that a novel chromosomal band in KF4 results from a deletion of 35-40 rDNA cistrons from the rDNA cluster. The significance of this finding to possible alterations in cell physiology and the ability to generate "petite" mutants is discussed.
Collapse
Affiliation(s)
- R Maleszka
- Molecular and Population Genetics Group, Research School of Biological Sciences, Australian National University, Canberra, ACT
| | | |
Collapse
|