Human RNA helicase A is homologous to the maleless protein of Drosophila.

RNA helicase A is an abundant nuclear enzyme of HeLa cells that unwinds double-stranded RNA in a 3' to 5'direction (Lee, C. G., and Hurwitz, J. (1992) J. Biol. Chem. 267, 4398-4407). A complementary DNA (cDNA) clone expressing RNA helicase A was isolated by screening a human cDNA library with polyclonal antibodies produced against the purified protein. The deduced amino acid sequence from this clone showed that RNA helicase A is a member of the DEAH family of proteins thought to be helicases. Sequence comparison among all known proteins of the DEAH family revealed that the highest homology was between RNA helicase A and the maleless protein (MLE) of Drosophila. There was 49% identity and 85% similarity throughout the overall primary sequences of both proteins, suggesting that RNA helicase A is the human counterpart of Drosophila MLE. Polyclonal antibodies against Drosophila MLE recognized RNA helicase A in crude nuclear extracts of HeLa cells as well as the purified protein. A recombinant RNA helicase A containing 6 histidine residues at the NH2 terminus was expressed in Sf9 cells using a baculovirus vector. The protein isolated from insect cells and the enzyme purified from HeLa cells exhibited identical RNA helicase and RNA-dependent ATPase activities.