[Rpn4p is a positive and negative transcriptional regulator of the ubiquitin-proteasome system]

Ubiquitin-proteasome proteolytic system participates in metabolism of the majority of intracellular proteins and regulation of key cellular processes in eukaryotes. While the structure and functioning of this system is studied rather well, a little is known about regulation of its genes expression. At present time, the only regulatory system of transcription of proteasome genes is found in the yeast Saccharomyces cerevisiae. This system includes Rpn4p-proteasome-associated transcriptional regulator and its binding site called PACE (Proteasome Associated Control Element). To learn more about function of Rpn4p as a transcriptional regulator, there are following questions: 1) is the Rpn4p regulator for PACE-containing genes which encode for components of protein ubiquitinylation system 2) what is the contribution of Rpn4p in stress-activated level of mRNA of proteasome genes. In this work, using semiquantitative RT-PCR we have shown that deletion of RPN4 gene leads to decreasing in mRNA level of the genes of ubiqitination system RAD6, RAD23 and CDC48, while UBI4 mRNA level is increased in this strain. In the presence of alkylating agent methyl methanesulfonate or under heat shock we observed Rpn4 p-dependent elevation of mRNA level of the proteasomal genes RPT4 and RPNS. At the same time, CDC48 mRNA level is decreased in wild type yeast strain upon methyl methanesulfonate treatment. These data indicate that under normal or stress conditions Rpn4p may act as an activator or repressor for the genes of the ubiquitin-proteasome system.