The role of the proteasomal ATPases and activator monoubiquitylation in regulating Gal4 binding to promoters

Periodate-triggered cross-linking reveals Sug2/Rpt4 as the molecular target of a peptoid inhibitor of the 19S proteasome regulatory particle

This study describes the identification of the protein target of the first chemical inhibitor (RIP-1) of the 19S regulatory particle (RP) of the 26S proteasome. Periodate-triggered chemical cross-linking of DOPA-conjugated RIP-1 and the 26S proteasome identified Sug2/Rpt4, one of the six ATPases in the 19S RP as the molecular target of RIP-1. The specificity of RIP-1 for Sug2/Rpt4 was demonstrated by examining cross-linking reactions with each ATPase of the 19S RP. RIP-1 should provide a useful biological tool to probe the various biological roles of Rpt4.

Dynamics of the hypoxia-inducible factor-1-vascular endothelial growth factor promoter complex

Some transactivator-promoter complexes are highly dynamic due to active disruption of the complex by proteolytic or nonproteolytic mechanisms, and this appears to be an important mechanism by which their activity is governed tightly and eventually terminated. However, the generality of these mechanisms is unclear. In this report, we address the dynamics of hypoxia-inducible factor-1 (HIF-1) binding to the vascular endothelial growth factor promoter. HIF-1 is a heterodimeric transcription factor whose activity is triggered by an increase in HIF-1alpha levels in hypoxic cells. A "competition ChIP" assay is employed to demonstrate that HIF-1alpha forms a kinetically stable complex with the native vascular endothelial growth factor promoter that has a half-life in excess of 1 h. Thus, HIF-1 activity does not require rapid proteolytic turnover of the promoter-bound transactivator, nor is the activator-promoter complex constantly disassembled by chaperones. However, we do find that after cessation of the inducing signal, HIF-1 activity is slowly returned to basal levels by proteasome-mediated proteolysis of the promoter-bound HIF-1alpha protein.

Identification of a peptoid inhibitor of the proteasome 19S regulatory particle

The first chemical inhibitor of the 19S Regulatory Particle (RP) of the proteasome is described. The molecule was identified by screening a library of nucleoside-capped peptoids for binding to the yeast 26S proteasome in a crude extract. The hit was resynthesized and shown to block 19S RP-mediated protein unfolding in vitro and proteasome-mediated turnover of p27 in HeLa cells.