Heat shock-induced alterations in phosphorylation of the largest subunit of RNA polymerase II as revealed by monoclonal antibodies CC-3 and MPM-2

The phosphorylation of the carboxy-terminal domain of the largest subunit o f RNA polymerase II plays an important role in the regulation of transcript ional activity and is also implicated in pre-mRNA processing. Different str esses, such as a heat shock, induce a marked alteration in the phosphorylat ion of this domain. The expression of stress genes by RNA polymerase II, to the detriment of other genes, could be attributable to such modifications of the phosphorylation sites. Using two phosphodependent antibodies recogni zing distinct hyperphosphorylated forms of RNA polymerase II largest subuni t, we studied the phosphorylation state of the subunit in different species after heat shocks of varying intensities. One of these antibodies, CC-3, p referentially recognizes the carboxy-terminal domain of the largest subunit under normal conditions, but its reactivity is diminished during stress. I n contrast, the other antibody used, MPM-2, demonstrated a strong reactivit y after a heat shock in most species studied. Therefore, CC-3 and MPM-2 ant ibodies discriminate between phosphoisomers that may be functionally differ ent. Our results further indicate that the pattern of phosphorylation of RN A polymerase II in most species varies in response to environmental stress.