Isolation of the positive-acting regulatory gene PHO4 from Saccharomyces cerevisiae.

We have isolated a 10.2-kb fragment of yeast DNA from a genomic library of recombinant centromeric YCp50 plasmids, which complements a mutation in the PHO4 gene of Saccharomyces cerevisiae. The identity of the PHO4 gene on this plasmid was established by integration of a subfragment into the PHO4 region of the yeast chromosome. Analysis of a series of plasmid subclones covering different regions of the original yeast DNA insert localized the PHO4 gene within a 2.25-kb sequence. Southern hybridization of total genomic DNA prepared from wild-type strains and from integrative transformants show that the PHO4 gene consists of unique yeast DNA sequences and is present at a single copy in the S. cerevisiae genome. RNA blot hybridization mapping of transcripts within this genomic region identify the PHO4 transcript as a 1.7-kb, low-abundancy, constitutively expressed and polyadenylated RNA.