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 and 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). The ATPase and/or helicase activity of RH;I is required for CREB-dependent transcription. 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 protein sequence of this region contains six hydrophobic residues and is unique to RHA homologues and well conserved. A mutant with this region deleted from full-length RHA decreased transcriptional activity in CREB-dependent transcription. In addition, mutational analyses revealed that several tryptophan residues in MTAD are important for the interaction with Pol II and transactivation, These mutants had ATP binding and ATPase activities comparable to those of wild-type RHA. A mutant lacking ATP binding activity mas still able to interact with Pol II. In CREB-dependent transcription, the transcriptional activity of each of these mutants was less than that of wild-type RHA, The activity of the double mutant lacking both functions was significantly lower than that of each mutant alone, and the double mutant had a dominant negative effect. These results suggest that RHA could independently regulate (CREB-dependent transcription either through recruitment of Pol II or by ATP-dependent mechanisms.