Identification of chromosomal location of yeast DNA from hybrid plasmid pYelueu10

Abstract

THERE is strong evidence to suggest that some genes of baker' yeast Saccharomyces cerevisiae can be expressed in Escherichia coli when cloned on plasmid or phage vectors^1,2. This conclusion is based on the observation that hybrid plasmids and bacteriophage carrying specific fragments of yeast nuclear DNA can complement certain auxotrophic mutations in the E. coli genome. Complementation alone, however, is not sufficient to prove that the cloned DNA contains a yeast gene equivalent to the defective bacterial gene. One aspect of the identification of any cloned DNA is the identification of its chromosomal origin. We present here a method for the identification of the chromosomal origin of cloned yeast DNA using hybridisation to DNA from yeast strains aneuploid for a single chromosome. Using this method we have confirmed the chromosomal location of the DNA of a yeast hybrid plasmid (pYeleu1O) presumed to contain sequences coding for the leucine biosynthetic enzyme β-isopropylmalate dehydrogenase, the leu2 gene of yeast.