Rpb4, a non-essential subunit of core RNA polymerase II of Saccharomyces cerevisiae is important for activated transcription of a subset of genes

A major role in the regulation of eukaryotic protein-coding genes is played by the gene-specific transcriptional regulators, which recruit the RNA pol ymerase II holoenzyme to the specific promoter. Several components of the m ediator complex within the holoenzyme also have been shown to affect activa tion of different subsets of genes. Only recently has it been suggested tha t besides the largest subunit of RNA polymerase Il, smaller subunits like R pb3 and Rpb5 may have regulatory roles in expression of specific sets of ge nes. We report here, the role of Rpb4, a non-essential subunit of core RNA polymerase II, in activation of a subset of genes in Saccharomyces cerevisi ae. We have shown below that whereas constitutive transcription is largely unaffected, activation from various promoters tested is severely compromise d in the absence of RPB4. This activation defect can be rescued by the over expression of cognate activators. We have localized the region of Rpb4 invo lved in activation to the C-terminal 24 amino acids. We have also shown her e that transcriptional activation by artificial recruitment of the TATA-bin ding protein (TBP) to the promoter is also defective in the absence of RPB4 . Surprisingly, the overexpression of RPB7 (the interacting partner of Rpb4 ) does not rescue the activation defect of all the promoters tested, althou gh it rescues the activation defect of the heat shock element-containing pr omoter and the temperature sensitivity associated with RPB4 deletion. Overa ll, our results indicate that Rpb4 and Rpb7 play independent roles in trans criptional regulation of genes.