The Saccharomyces cerevisiae chromatin-modifying protein Chd1
interacts with the transcription elongation factors Rtf1 and
Spt5.
Patrick J. Costa (1), Derek L. Lindstrom (2), Hien G. Tran
(3), Kelli L. Roinick (1), Rajna Simic (1), Alexander D. Johnson (3),
Grant A. Hartzog (2), Karen M. Arndt (1)
(1) Biological
Sciences, University of Pittsburgh, 269 Crawford Hall, Pittsburgh, PA
15260, USA; (2) Department of MCD Biology, University of California,
Santa Cruz, CA 95064; (3) Department of Biochemistry and Biophysics,
University of California, San Francisco, CA 94143
Transcription
elongation is an important regulatory step in gene expression. The
product of the RTF1 gene interacts functionally and physically
with proteins that regulate the elongation properties of RNA polymerase
II. In addition, rtf1 mutations confer phenotypes often
indicative of transcription elongation defects. We have recently shown
that Rtf1 is a member of the RNA polymerase II-associated Paf1 complex
and that this complex interacts with the conserved elongation factors
Spt5-Spt4 and Spt16-Pob3. To further elucidate the function of Rtf1, we
performed a two-hybrid screen for Rtf1-interacting proteins. We found
that the chromatin-modifying protein Chd1 interacts with Rtf1 and that
Chd1 levels are reduced in an rtf1 mutant strain, indicating the
existence of a complex containing Rtf1 and Chd1. Our genetic results are
in agreement with our biochemical studies. Most notably, in two genetic
screens, we found that mutations in CHD1 can suppress the growth
defect conferred by a pob3 mutation and the cold sensitivity
caused by an spt5 mutation. The genetic interaction between Chd1
and Spt5 correlates with a physical interaction between these proteins.
Together, these results suggest that a protein complex containing
members of the Paf1 complex, Spt5-Spt4, Spt16-Pob3, and Chd1 regulates
transcription elongation by RNA polymerase II. In support of this idea,
we have recently found that Chd1, Rtf1, and Spt5 localize to the coding
regions of actively transcribed genes.
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