cytochromes-c1 and Chromosome-Deletion

The nuclear gene for cytochrome c1 in Saccharomyces cerevisiae (CYT1) was localized on chromosome XV. Its upstream region was identified by functional complementation. Fusion to the lacZ reporter gene on a CEN plasmid allowed study of the effect of carbon sources and of specific deletion mutations on expression of the gene in yeast transformants. Detailed promoter analysis combined with expression studies in recipient strains defective in regulatory genes identified cis-acting sites and transcription factors involved in the regulated expression of the cytochrome c1 gene. These analyses showed that, in the presence of glucose, transcription of CYT1 is positively controlled by oxygen, presumably through the haem signal, and mediated by the HAP1-encoded transactivator. It is additionally regulated by the HAP2/3/4 complex which mediates gene activation mainly under glucose-free conditions. Basal transcription is, in part, effected by CPF1, a centromere and promoter-binding factor.

Topics: Base Sequence; beta-Galactosidase; Binding Sites; Chromosome Deletion; Chromosome Mapping; Chromosomes, Fungal; Cloning, Molecular; Cytochromes c1; DNA, Fungal; Gene Expression Regulation, Fungal; Genes, Fungal; Genes, Regulator; Glucose; Heme; Molecular Sequence Data; Oxygen; Promoter Regions, Genetic; Recombinant Fusion Proteins; Regulatory Sequences, Nucleic Acid; Saccharomyces cerevisiae; Sequence Homology, Nucleic Acid; Transcription Factors; Transcription, Genetic; Transcriptional Activation

Mutants arising spontaneously from sporulated cultures of certain strains of yeast, Saccharomyces cerevisiae, contained deletions of the CYC1 gene which controls the primary structure of iso-1-cytochrome c. At least 60 different kinds of deletions were uncovered among the 104 deletions examined and these ranged in length from those encompassing only two adjacent point mutants to those encompassing at least the entire CYC1 gene. X-ray-induced recombination rates of crosses involving these deletions and cyc1 point mutants resulted in the assignment of 211 point mutants to 47 mutational sites and made it possible to unambiguously order 40 of these 47 sites. Except for one mutant, cyc1-15, there was a strict colinear relationship between the deletion map and the positions of 13 sites that were previously determined by amino acid alterations in iso-1-cytochromes c from intragenic revertants.

Topics: Chromosome Aberrations; Chromosome Deletion; Chromosome Mapping; Cytochrome c Group; Cytochromes c1; Genes; Mutation; Saccharomyces cerevisiae