REGULATION OF POLY(A) SITE CHOICE OF SEVERAL YEAST MESSENGER-RNAS

Several yeast genes produce multiple transcripts with different 3'-end s. Of these, four genes are known to produce truncated transcripts tha t end within the coding sequence of longer transcripts: CBP1, AEP2/ATP 13, RNA 14 and SIR1, It has been shown that the level of the truncated CBP1 transcript increases during the switch to respiratory growth whi le that of the full-length transcript decreases. To determine whether this phenomenon is unique to CBP1, northern analysis was used to deter mine whether the levels of other truncated transcripts are regulated s imilarly by carbon source. The levels of the shortest transcripts of A EP2/ATP13 and RNA 14 increased during respiration while the shortest S IR1 transcript remained constant. However, two longer SIR1 transcripts were regulated reciprocally by carbon source. Mapping the 3'-ends of each transcript by sequencing partial cDNA clones revealed multiple 3' -ends for each transcript. Examination of the sequences surrounding th e 3'-ends of the induced transcripts failed to identify a consensus se quence but did reveal weak putative 3'-end formation signals in all of the transcripts. Similarly, no consensus sequence was found when the sequences surrounding the 3'-ends of the longest transcripts were comp ared, but again weak putative 3'-end formation signals were identified . These data are suggestive of carbon source regulation of alternative poly(A) site choice in yeast.