Getting started: a role for RPB4 in the growth response to fresh medium.
Warren Heideman, Matthew Slattery, Dominic Porcaro, Dritan Liko
Pharmaceutical Sciences, University of Wisconsin, 777 Highland Ave, Madison, WI, 53705, United States
It is common to inoculate yeast into new medium from an overnight culture. We are studying the mechanisms that allow yeast to quickly resume log phase growth when transferred to fresh medium (YPD). This requires both growth of cellular structures and cell cycle progression. Among the genes induced by YPD are CLN3 and CDC28, which promote proliferation. A sequence motif upstream of both CLN3 and CDC28 is conserved between Saccharomyces species and forms a protein/DNA complex in gel shift experiments. Rpb4, a non-essential subunit of RNA polymerase II, is necessary for both the formation of this protein/DNA complex, and the induction of CLN3, and CDC28 by YPD. RPB4 deletion also blocks the rapid increase in poly (A)+ RNA observed immediately after addition of fresh medium. Cells lacking Rpb4 grow slowly in proliferation and cell mass, suggesting that Rpb4 plays a role in coordinating transcription of genes needed for rapid growth and cell division. Rpb4-dependent induction of CLN3 and CDC28 requires glucose metabolism and is blocked by mutations in PFK1, PFK2, and CDC19, indicating that metabolism initiates the Rpb4-dependent gene induction. YPD increases phosphorylation of Rpb1, the largest subunit of RNA polymerase II. As a RNA Pol II subunit, Rpb4 is in a position to regulate a large number of genes. Microarray experiments confirm this; loss of Rpb4 produces a fall in cell wall and organelle biosynthesis, metabolism, and cell cycle progression transcripts.
Return to YGM 2004 Home at SGD