POLY(A) SIGNALS CONTROL BOTH TRANSCRIPTIONAL TERMINATION AND INITIATION BETWEEN THE TANDEM GAL10 AND GAL7 GENES OF SACCHAROMYCES-CEREVISIAE

We have investigated transcriptional interactions between the GAL10 an d GAL7 genes of Saccharomyces cerevisiae. Both genes are part of the g alactose (GAL) gene cluster which is transcriptionally activated to hi gh levels in the presence of galactose, Since GAL7 is positioned downs tream of GAL10 and both genes are expressed co-ordinately at high leve ls, the possibility that GAL10 transcription influences GAL7 was analy sed. Using transcriptional run-on assays, we show that high levels of polymerase are found in the 600 bp GAL10-7 intergenic region that accu mulate over the GAL7 promoter. Furthermore, GAL7 transcription is enha nced when the GAL10 upstream activating sequence (UAS(G)) is deleted, indicating that interference between GAL10 and GAL7 is likely to occur in the chromosomal locus. Deletions in the GAL10 poly(A) signal resul t in complete inactivation of the GAL7 promoter and cause a dramatic i ncrease in bi-cistronic GAL10-7 mRNA, predominantly utilizing the down stream, GAL7 poly(A) site. These data demonstrate a pivotal role for t he GAL10 poly(A) site in allowing the simultaneous expression of GAL10 and GAL7, In effect, this RNA processing signal has a direct influenc e on both transcriptional termination and initiation.