THE YEAST TRANSCRIPTION TERMINATOR FOR RNA-POLYMERASE-I IS DESIGNED TO PREVENT POLYMERASE SLIPPAGE

A transcription terminator for RNA polymerase I (poll) in the yeast, S accharomyces cerevisiae, is composed of two essential elements, the 11 bp binding site for Reb1p and an upstream T-rich element coding for th e last 10-12 nucleotides of the terminated transcript. We now show tha t, if the upstream element is changed to homopolymer T residues, poll undergoes iterative slippage, long poly(U) tails are added to the tran script, and termination is impaired, Reinsertion of one or two non-T r esidues within a critical region prevents iterative slippage and reins tates termination, A survey of naturally occurring terminators reveals that many contain T-rich upstream regions with non-T residues situate d appropriately to prevent slippage, We discuss the possibility that t he first step in slippage, backward sliding of both the transcript and the catalytic center of the polymerase, may be an obligatory step in the normal termination process.