Nap1 links transcription elongation, chromatin assembly and mRNP biogenesis

Center for Cell Signaling, University of Virginia, Charlottesville, VA 22908, USA

^* To whom correspondence should be addressed. Email: lfp2n{at}virginia.edu.

	Abstract

Chromatin remodeling is central to the regulation of transcription elongation. We demonstrate that the conserved Saccharromyces cerevisiae histone chaperone Nap1 associates with chromatin. We show that Nap1 regulates transcription of PHO5, and the increase in transcript level and the higher phosphatase activity plateau observed in nap1 cells suggest that the net function of Nap1 is to facilitate nucleosome reassembly during transcription elongation. To further our understanding of histone chaperones in transcription elongation, we identified factors that regulate the function of Nap1 in this process. One factor investigated is the essential mRNA export and TREX complex component, Yra1. Nap1 interacts directly with Yra1 and genetically with other TREX components and the mRNA export factor Mex67. Additionally we show that the recruitment of Nap1 to the coding region of actively transcribed genes is Yra1 dependent and its recruitment to promoters is TREX independent. These observations suggest that Nap1 functions provide a new connection between transcription elongation, chromatin assembly and mRNP biogenesis.