ALTERED RESPONSE TO GROWTH-RATE CHANGES IN KLUYVEROMYCES-LACTIS VERSUS SACCHAROMYCES-CEREVISIAE AS DEMONSTRATED BY HETEROLOGOUS EXPRESSION OF RIBOSOMAL PROTEIN-59 (CRY1)

We report the cloning, characterization and preliminary analysis of the regulation of the gene coding for ribosomal protein 59 (RP59) from the budding yeast Kluyveromyces lactis. The RP59 gene is present as a single copy, contains an intron within the amino terminal coding portion of the gene, and harbors conserved S. cerevisiae splicing signals. Sequence elements upstream of the transcriptional start site are homologous to UAS(RPG), known to regulate the transcription of numerous genes in S. cerevisiae via their interaction with the trans-activating factor RAP1. These elements are necessary for transcription of RP59 in both K.lactis and S.cerevisiae hosts. UAS(RPG) in S.cerevisiae rp genes also modulate the transcription of rp RNA synthesis in response to a growth rate upshift. In K.lactis, the RP59 gene does not respond to growth rate upshift. Reciprocal expression of RP59 and CRY1 in heterologous hosts demonstrates that glucose upshift occurs in S.cerevisiae but not K.lactis. These results demonstrate that a factor or factors required for growth upshift are lacking in K.lactis, and provide further evidence that the UAS(RPG) are sufficient signals for modulating this response.