SCREENING AND IDENTIFICATION OF YEAST SEQUENCES THAT CAUSE GROWTH-INHIBITION WHEN OVEREXPRESSED

To isolate genes that negatively regulate cell growth, we constructed a galactose-inducible expression library with partially digested Sacch aromyces cerevisiae genomic DNA fragments inserted downstream of the G AL10 promoter. In all, 240 000 yeast transformants were screened for l ethality on galactose medium. From 17 such transformants identified, 1 6 nonoverlapping DNA sequences were obtained. Restriction mapping and determination of DNA sequences adjacent to the GAL10 promoter indicate d that the inserts encoded part or all of the URA2, RBP1, TPK3, SAC7, BOI1, and BNI1 genes, and also open reading frames (ORFs) from chromos omes IV, V, IX, XI, and XIII. Some of the identified sequences lacked the amino-terminal sequences of the ORFs, suggesting that truncated fo rms of the proteins might be necessary for growth inhibition. The sequ ence of the pGA108 insert was highly homologous to the telomeric X-ele ment and contained an ARS consensus sequence, suggesting a possible gr owth inhibitory effect of an RNA molecule. Overexpression of the BNI1 Delta N and BOI1 Delta N genes, which lacked aminoterminal sequences, was associated with phenotypes similar to those of mutants defective i n bud formation. Overexpression of the GIN4 and GIN12 sequences induce d elongated buds and a G2/M arrest-like phenotype, respectively. The p henotypes induced by the overexpression of our cloned sequences could result from either a dominant-positive or a dominant-negative effect a nd, unexpectedly, in one case from an effect of an RNA.