The KlCYC1 gene, a downstream region for two differentially regulated transcripts.

KlCYC1 encodes for cytochrome c in the yeast Kluyveromyces lactis and is transcribed in two mRNAs with different 3'-processing points. This is an uncommon transcription mechanism in yeast mRNAs. The 3' sequence encompassing the whole region that is needed to produce both mRNAs is analysed. We have determined identical processing points in K.lactis and in Saccharomyces cerevisiae cells transformed with KlCYC1; positions 698 and 1092 (with respect to the TAA) are the major polyadenylation points. This shows that the cis-elements present in the KlCYC1 3'-untranslated region (3'-UTR) direct a processing mechanism that has been conserved in yeast. In K. lactis there is a high predominance of the shorter transcript (1.14 kb) only at the initial logarithmic growth phase. Interestingly, this growth phase-dependent regulation of 3'-UTR processing is lost when the gene is expressed in S. cerevisiae. Copyright 2001 John Wiley & Sons, Ltd.