MUTANTS OF YEAST DEFECTIVE IN ISO-1-CYTOCHROME c

[摘要] A medium containing chlorolactate has been devised to enrich for mutants that are unable to utilize lactate for growth, and therefore that may be defective in cytochrome c . Complementation tests of 6,520 chlorolactate-resistant mutants that were obtained spontaneously or induced with UV , ICR-170 , or nitrosoimidazolidone resulted in the identification of 195 mutations at the cycl locus, which controls the primary structure of iso-1-cytochrome c . These 195 mutants, with 16 cycl mutants previously isolated, were examined for total cytochrome c by spectroscopic methods, growth on lactate medium, suppressibility by defined nonsense suppressor, mutational sites by x-ray-induced recombination, ability to revert, and in 86 cases, whether intragenic revertants contain altered iso-1-cytochrome c . Except for the deletion mutant cycl-1 , all of thb mutants appeared to contain single-site mutdons that could be assigned to at least 35 different sites within the gene. The cycl mutants either completely lacked iso-1-cytochrome c or contained iso-1-cytochromes c that were completely or partially nonfunctional. In spite of the fact that the cyd mutants obtained by the chlorolactate procedure were selected on the basis of defective function, 68% appeared to completely lack iso-1-cytochrome c . The remaining cycl mutants contained below normal amounts of iso-1-cytochromes c . Studies at several incubation temperatures indicated that these nonfunctional iso-1-cytochromes c were thermolabile. It is suggested that the predominant means for abolishing iso-1-cytochrome c by mutations are either through a complete loss, such as produced by chain terminating codons, or impairments through drastic changes of tertiary structure which lead to instability and thermolability.

[学科分类] 医学（综合）