Transcription termination by RNA polymerase III in fission yeast - A genetic and biochemically tractable model system

In order for RNA polymerase (pol) III to produce a sufficient quantity of R NAs of appropriate structure, initiation, termination, and reinitiation mus t be accurate and efficient. Termination-associated factors have been shown to facilitate reinitiation and regulate transcription in some species. Sup pressor tRNA genes that differ in the dT(n) termination signal were examine d for function in Schizosaccharomyces pombe, We also developed an S. pombe extract that is active for tRNA transcription that is described here for th e first time. The ability of this tRNA gene to be transcribed in extracts f rom different species allowed us to compare termination in three model syst ems. Although human pol III terminates efficiently at 4 dTs and S. pombe at 5 dTs, Saccharomyces cerevisiae pol III requires 6 dTs to direct comparabl e but lower termination efficiency and also appears qualitatively distinct. Interestingly, this pattern of sensitivity to a minimal dT(n) termination signal was found to correlate with the sensitivity to alpha-amanitin, as S. pombe was intermediate between human and S. cerevisiae pols III. The resul ts establish that the pols III of S. cerevisiae, S. pombe, and human exhibi t distinctive properties and that termination occurs in S. pombe in a manne r that is functionally more similar to human than is S. cerevisiae.