The results shown in Fig

The results shown in Fig. cdk9 mRNAs. Interestingly, DRB and siRNA reduced the levels of ICP22 but not those of other gene products. In addition, cdk9 and ICP22 appeared to colocalize with RNA Pol II in wild-type-virus-infected cells but not in UL13-infected cells. We conclude that cdk9 plays a critical role in the optimization of expression of genes regulated by ICP22 and that one function of cdk9 in HSV-1-infected cells may be to bring ICP22 into the RNA Pol II transcriptional complex. The studies Aceclofenac described in this report center on the role of infected cell protein Aceclofenac 22 (ICP22), an (immediate early) protein in Aceclofenac viral replication. Mutants lacking ICP22 yield reduced levels of viral progeny in a cell-type-dependent manner (36). The protein appears to perform several functions (24). A key function expressed by the carboxyl-terminal domain name (CTD) of ICP22 in conjunction with the viral UL13 protein kinase is to enhance the synthesis of a subset of late (2) proteins exemplified by the products of the UL38, UL41, and US11 genes (2, 24, 31, 37). In earlier studies, this laboratory reported that ICP22 and the UL13 protein kinase mediate the activation of cdc2 and degradation of its partners, cyclins A and B (3, 4). cdc2 and its new partner, the viral DNA polymerase accessory factor (UL42), bind topoisomerase II in an ICP22-dependent manner (1, 4). In addition, ICP22 and UL13 mediate an intermediate phosphorylation of the carboxyl terminus of RNA polymerase II (Pol II) in Vero cells (14, 18, 34, 35). Subsequent studies designed to elucidate the conversation of ICP22 with RNA Pol II led to the discovery that ICP22 actually interacts with cyclin-dependent kinase 9 (cdk9) and that the protein Rabbit polyclonal to GnT V complex made up of ICP22 and cdk9 phosphorylated the CTD of RNA Pol II in a viral US3 protein kinase-dependent fashion in vitro (8). These studies also showed that this CTD of RNA Pol II fused to glutathione em S /em -transferase was phosphorylated in reaction mixtures made up of ICP22 or cdk9 immunoprecipitated from lysates of wild-type parent computer virus- or UL13 mutant computer virus- but not from US3 mutant virus-infected cells (8). The levels of cdk9 and its partner, cyclin T, were unaltered throughout the replicative cycle. These experiments placed ICP22 and cdk9 in a complex with the CTD of RNA Pol II. At the same time, we confirmed the requirement of ICP22 and the UL13 protein kinase in the posttranslational modification of RNA Pol II that alters its electrophoretic mobility, while US3 kinase appears to play a similar role but in a cell type-dependent fashion (8). The focus of this report is around the role of cdk9 in the expression of the subset of viral genes regulated by ICP22. We found the following relevant to this report. cdk9 is usually a Ser/Thr proline-directed kinase that shares 47% homology with other cdk’s (22). It was originally designated PITALRE because of its similarity to the PSTAIRE-like cyclin binding motif of cdc2, a motif that has been identified in all cdk-related kinases (20, 23). cdk9 is usually ubiquitously expressed and exists as two isoforms, i.e., cdk942 and cdk955. cdk955 contains a 13-kDa N-terminal Pro-Gly rich extension and is expressed from a TATA-containing promoter, whereas cdk942 is not (37). The ratio of cdk942/cdk955 is usually cell type dependent and most likely regulated in a tissue-dependent manner (19, 37, 38). However, both cdk9 isoforms have been found to localize to the nucleus (27). cdk9 interacts with a variety of T-type cyclins, T1, T2a, T2b, and cyclin K (10, 26). cdk9 and its cyclin T partners bind together and are referred to as positive transcription elongation factor b (P-TEFb). The various complexes.