Skip to main content
. Author manuscript; available in PMC: 2009 Dec 3.
Published in final edited form as: Mol Cell. 2006 Jun 9;22(5):633–644. doi: 10.1016/j.molcel.2006.04.009

Figure 7.

Figure 7

A Model for Pol III Repression

In favorable growth conditions, the Pol III system (Pol III, TFIIIB, and TFIIIC) forms an initiation complex and commits to RNA synthesis (Active). During elongation, active Pol III may displace (arrow) TFIIIC from the A/B box (semiopaque TFIIIC). TFIIIC may be fully ejected from the template, or remain tethered to the locus, either through interactions with the terminator (via Tfc6) or other members of the Pol III system. In exponential growth, Maf1 is largely phosphorylated, attenuating a small portion of Pol III (semiopaque Maf1). Nutrient deprivation or stress promotes Maf1 dephosphorylation, increasing the proportion of Maf1 molecules in association with Pol III and Pol III targets (Inactive, opaque Maf1). This association attenuates Pol III targets by an unknown mechanism. Pol III inactivity lowers its effective interaction (ChIP) with target DNA, allowing full TFIIIC occupancy. During the acute phase of repression, the interaction between TFIIIC and TFIIIB increases. However TFIIIB slowly releases from certain Pol III targets during prolonged repression (data not shown). Maf1 may directly inhibit Pol III and/or promote TFIIIB inactivation (red asterisk).