To continue the systematic examination of the physical and genetic organization of an entire Saccharomyces cerevisiae chromosome, the DNA from the CEN1-ADE1-CDC15 region from chromosome I was isolated and characterized. Starting with the previously cloned ADE1 gene (J. C. Crowley and D. B. Kaback, J. Bacteriol. 159:413-417, 1984), a series of recombinant lambda bacteriophages containing 82 kilobases of contiguous DNA from chromosome I were obtained by overlap hybridization. The cloned sequences were mapped with restriction endonucleases and oriented with respect to the genetic map by determining the physical positions of the CDC15 gene and the centromeric DNA (CEN1). The CDC15 gene was located by isolating plasmids from a YCp50 S. cerevisiae genomic library that complemented the cdc15-1 mutation. S. cerevisiae sequences from these plasmids were found to be represented among those already obtained by overlap hybridization. The cdc15-1-complementing plasmids all shared only one intact transcribed region that was shown to contain the bona fide CDC15 gene by in vitro gene disruption and one-step replacement to delete the chromosomal copy of this gene. This deletion produced a recessive lethal phenotype that was also recessive to cdc15-1. CEN1 was located by finding a sequence from the appropriate part of the cloned region that stabilized the inheritance of autonomously replicating S. cerevisiae plasmid vectors. Finally, RNA blot hybridization and electron microscopy of R-loop-containing DNA were used to map transcribed regions in the 23 kilobases of DNA that went from CEN1 to CDC15. In addition to the transcribed regions corresponding to the ADE1 and ADC15 genes, this DNA contained five regions that gave rise to polyadenylated RNA, at least two regions complementary to 4S RNA species, and a Ty1 transposable element. Notably, a higher than average proportion of the DNA examined was transcribed into RNA.
The CDC25 protein of Saccharomyces cerevisiae promotes exchange of guanine nucleotides bound to ras.