Dual roles of RNA helicase A in CREB-dependent transcription

RNA helicase A (RHA) is a member of an ATPase/DNA and RNA helicase family a nd is a homologue of Drosophila. maleless protein (MLE), which regulates X- linked gene expression. RHA is also a component of holo-RNA polymerase II ( PoI II) complexes and recruits Pol II to the CREB binding protein (CBP). Th e ATPase and/or helicase activity of RH;I is required for CREB-dependent tr anscription. To further understand the role of RI-IA on gene expression, we have identified a 50-amino-acid transactivation domain that interacts with PoI II and termed it the minimal transactivation domain (MTAD). The protei n sequence of this region contains six hydrophobic residues and is unique t o RHA homologues and well conserved. A mutant with this region deleted from full-length RHA decreased transcriptional activity in CREB-dependent trans cription. In addition, mutational analyses revealed that several tryptophan residues in MTAD are important for the interaction with Pol II and transac tivation, These mutants had ATP binding and ATPase activities comparable to those of wild-type RHA. A mutant lacking ATP binding activity mas still ab le to interact with Pol II. In CREB-dependent transcription, the transcript ional activity of each of these mutants was less than that of wild-type RHA , The activity of the double mutant lacking both functions was significantl y lower than that of each mutant alone, and the double mutant had a dominan t negative effect. These results suggest that RHA could independently regul ate (CREB-dependent transcription either through recruitment of Pol II or b y ATP-dependent mechanisms.