ABSTRACT
There is a natural variation in the molecular structure of RNA polymerase A isolated from several genetically distant yeast species, Saccharomyces cerevisiae, Saccharomyces douglasii, Schizosaccharomyces pombe, and Candida tropicalis. Several biochemical criteria were used to identify their homologous polypeptide components. Based on these correlations, the minimal subunit composition of S. cerevisiae (and Saccharomyces carlsbergensis) RNA polymerase A was tentatively defined as A190, A135, A40, A27, A23, A19, and A14.5. Without the two Saccharomyces species, S. cerevisiae and S. douglasii, 7 of 13 polypeptides of enzyme A(A49, A43, A40, A34.5, A19, A14.5, and A14) differ slightly in molecular weight and can be resolved by electrophoresis on polyacrylamide gel. The RNA polymerase A isolated from the diploid interspecific hybrid contains all the polypeptides characteristic of the two parents. One meiotic segregant had a hybrid RNA polymerase A with five of the polymorphic polypeptides (A49, A43, A19, A14.5, and A14) coming from S. douglasii and two (A40 and A34.5) from S. cerevisiae. In three successive backcrosses with S. cerevisiae, all the genes for S. douglasii polypeptides were shown to recombine although parental ditype tetrads predominated in the four four-spored asci examined. Thus, the genes for the seven polymorphic polypeptides are not clustered: they lie on at least three different chromosomes.
Subject(s)
Ascomycota/enzymology , Candida/enzymology , DNA-Directed RNA Polymerases/genetics , Genetic Variation , RNA Polymerase I/genetics , Saccharomyces cerevisiae/enzymology , Saccharomyces/enzymology , Schizosaccharomyces/enzymology , Candida/genetics , Macromolecular Substances , Molecular Weight , Saccharomyces/genetics , Saccharomyces cerevisiae/genetics , Schizosaccharomyces/genetics , Species SpecificityABSTRACT
Eight UGA alleles have been obtained in S. cerevisiae. Two UGA alleles, ade5,7-143 and gal10-1, were isolated as forward mutations from wildtype. Six UGA alleles, arg4-2' (UGA), his5-2' (UGA), ilv3-1' (UGA), leu2'1' (UGA), lys1-1' (UGA), and asp5-1' (UGA), were derived from UAA alleles by selecting from revertants in the presence of UGA suppressors. With these 8 UGA alleles, two classes of UGA-specific suppressors can be distinguished. Suppressors in one class act upon all 8 allelqs ; while suppressors in the second class act upon all but 3 alleles : ade5,7-143, arg4-2' (UGA), and gal10-1.
Subject(s)
Codon , Genetic Code , Mutation , RNA, Messenger , Saccharomyces cerevisiae , Suppression, Genetic , Adenine Nucleotides , Alleles/radiation effects , Guanine Nucleotides , Mutation/radiation effects , Radiation Genetics , Ultraviolet Rays , Uracil NucleotidesABSTRACT
Through use of tetrad, random spore, trisomic, and mitotic analysis procedures a large number of genes, including 48 new genetic markers, were studied for their locations on the genetic maps of the yeast Saccharomyces cerevisiae. Eighteen new centromere linked genes were discovered and all but one was located on various ones of the 16 previously-established chromosomes. Five fragments of linked genes were also assigned to chromosomes; four were located on known chromosomes while the fifth determined one arm of a new chromosome. The experiments indicate that seventeen is likely to be the haploid chromosome number in this yeast. Most chromosomes have been established by genetic means to be metacentric and their genetic lengths vary from 5 cM to approximately 400 cM. Functionally-related sets of genes generally were found to be dispersed over the genome.
