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Chromatin remodeling can facilitate the recruitment of RNA polymerase II (Pol II) to targeted promoters, as well as enhancing the level of transcription. Here, we describe a further key role for chromatin remodeling in transcriptional termination. Using a genetic screen in S. pombe, we identified the CHD-Mi2 class chromatin remodeling ATPase, Hrp1, as a termination factor. In S. cerevisiae, we show that transcriptional termination and chromatin structure at the 3' ends of three genes all depend on the activity of the Hrp1 homolog, Chd1p, either alone or redundantly with the ISWI ATPases, Isw1p, and Isw2p. We suggest that chromatin remodeling of termination regions is a necessary prelude to efficient Pol II termination.

We identify Rpa12p of RNA polymerase I (Pol I) as a termination factor. Combined analyses using transcription run-on, electron microscopy-visualized chromatin spreading and RT-PCR have been applied to the rRNA-encoding genes of Saccharomyces cerevisiae. These confirm that Pol I termination occurs close to the Reb1p-dependent terminator in wild-type strains. However, deletion mutants for the 3 end-processing enzyme Rnt1p or the Rpa12p subunit of Pol I both show Pol I transcription in the spacer. For ⌬rpa12, these spacer polymerases are devoid of nascent transcripts, suggesting they are immediately degraded. The homology of Rpa12p to the small subunit Rpb9p of Pol II and Rpc11p of Pol III, both implicated in transcriptional termination, points to a common termination mechanism for all three classes of RNA polymerase.

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