Yeast transcription elongation factor SPT5 associates with RNA polymerase I and RNA polymerase II directly.

Spt5 is a transcription factor conserved in all three kingdoms of life. Spt5 homologues from bacteria and archaea bind the largest subunit of their respective RNA polymerases. Here we demonstrate that Spt5 directly associates with RNA polymerase I (Pol I) and RNA polymerase II (Pol II) in yeast through its ...
central region containing conserved NGN and KOW domains. Deletion analysis of SPT5 supports our biochemical data, demonstrating the importance of the KOW domains in Spt5 function. Far Western blot analysis implicates A190 of Pol I as well as Rpb1 of Pol II in binding Spt5. Three additional subunits of Pol I may also participate in this interaction. One of these subunits, A49, has known roles in transcription elongation by Pol I. Interestingly, spt5 truncation mutations suppress the cold-sensitive phenotype of rpa49 strain which lacks the A49 subunit in the Pol I complex. Finally, we observed that Spt5 directly binds to an essential Pol I transcription initiation factor, Rrn3, and to the ribosomal RNA (rRNA). Based on these data we propose a model in which Spt5 is recruited to the rDNA early in transcription, and that it plays an important role in rRNA synthesis through direct binding to the Pol I complex.
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Date: Apr. 05, 2011
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