Transposition of the gene cluster CYC1-OSM1-RAD7 in yeast

Contrasting mutation rates in mitochondrial and nuclear genes of yeasts versus mammals

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.

A highly revertible cyc1 mutant of yeast contains a small tandem duplication

A mutant, cyc1-96, that reverts spontaneously at an extremely high rate, was uncovered after examining approximately 500 cyc1 mutants which lack or have defective iso-1-cytochrome c in the yeast Saccharomyces cerevisiae. Cloning and DNA sequencing of appropriate fragments revealed that the cyc1-96 mutation contained a 19 bp duplication whereas the spontaneously arising revertants contained the normal wild-type sequence. Because the 19 bp segment in the wild-type sequence is flanked by a 5 bp repeat and because the cyc1-96 mutation arose spontaneously, the 19 bp duplication may have arisen by slippage and misalignment during DNA synthesis. The high reversion rate was not diminished in strains containing the rad52 mutation, which generally reduces mitotic recombination, including recombination associated with the elimination of a segment of a long direct repeat. Thus the loss of segments from short and long duplications occur by different mechanisms. We suggest that the high reversion rates of cyc1-96 and other short duplications are due to misalignment errors during replication.

Transformation of yeast with synthetic oligonucleotides

Genomic DNA of the yeast, Saccharomyces cerevisiae, can be conveniently and specifically altered by transforming spheroplasts or lithium acetate-treated cells directly with synthetic oligonucleotides. Altered forms of iso-1-cytochrome c were generated by transforming a cyc1 mutant with oligonucleotides and selecting for at least partially functional revertants; the oligonucleotides contained a sequence that corrected the cyc1 mutation and produced additional alterations at nearby sites. Transformation has been accomplished with oligonucleotides as short as 20 nucleotides and with amounts as low as 100 micrograms. This method of site-directed mutagenesis in vivo has been used to produce alterations in the NH2-terminal region of iso-1-cytochrome c in which the NH2-terminal methionine is excised and the penultimate residue is acetylated.

Physical analysis of the COR region: a cluster of six genes in Saccharomyces cerevisiae

Six genes, CYC1, UTR1, UTR3, OSM1, tRNAGly, and RAD7, have been localized within an 8-kilobase region on chromosome X of the yeast Saccharomyces cerevisiae. The physical structures and the transcripts of these genes were identified by analyzing a normal strain and six deletion mutants by genomic blotting, transcriptional analysis, and gene disruption procedures. The well-studied CYC1 gene encodes iso-1-cytochrome c; the tRNAGly gene encodes a tRNA; deletion of OSM1 and RAD7 causes sensitivity to hypertonic medium and UV irradiation, respectively. There were no observable phenotypes in strains having deletions of the UTR1, UTR3, and tRNAGly gene. The high density of transcripts, with little or almost no intragenic regions, indicates that the chromosomal organization of S. cerevisiae resembles the chromosomal organization of procaryotes rather than higher eucaryotes.

Physical analysis of the COR region: a cluster of six genes in Saccharomyces cerevisiae

Six genes, CYC1, UTR1, UTR3, OSM1, tRNAGly, and RAD7, have been localized within an 8-kilobase region on chromosome X of the yeast Saccharomyces cerevisiae. The physical structures and the transcripts of these genes were identified by analyzing a normal strain and six deletion mutants by genomic blotting, transcriptional analysis, and gene disruption procedures. The well-studied CYC1 gene encodes iso-1-cytochrome c; the tRNAGly gene encodes a tRNA; deletion of OSM1 and RAD7 causes sensitivity to hypertonic medium and UV irradiation, respectively. There were no observable phenotypes in strains having deletions of the UTR1, UTR3, and tRNAGly gene. The high density of transcripts, with little or almost no intragenic regions, indicates that the chromosomal organization of S. cerevisiae resembles the chromosomal organization of procaryotes rather than higher eucaryotes.

Structure of chromosomal rearrangements induced by the FB transposable element in Drosophila

Examination of 10 chromosomal rearrangements induced by foldback transposable elements in Drosophila demonstrates that sequences located between two closely linked elements are frequently deleted. Rearrangement and recombination events occurring within or adjacent to a foldback element are also observed. The type and frequency of rearrangement generated depend on element structure and the organization of flanking DNA.

rme1 Mutation of Saccharomyces cerevisiae: map position and bypass of mating type locus control of sporulation

Sporulation in Saccharomyces cerevisiae normally occurs only in MATa/MAT alpha diploids. We show that mutations in RME1 bypassed the requirements for both a and alpha mating type information in sporulation and therefore allowed MATa/MATa and MAT alpha/MAT alpha diploids to sporulate. RME1 was located on chromosome VII, between LEU1 and ADE6.

rme1 Mutation of Saccharomyces cerevisiae: map position and bypass of mating type locus control of sporulation

Sporulation in Saccharomyces cerevisiae normally occurs only in MATa/MAT alpha diploids. We show that mutations in RME1 bypassed the requirements for both a and alpha mating type information in sporulation and therefore allowed MATa/MATa and MAT alpha/MAT alpha diploids to sporulate. RME1 was located on chromosome VII, between LEU1 and ADE6.