A putative mammalian RNA helicase with an arginine-serine-rich domain colocalizes with a splicing factor

We have cloned a rat cDNA whose deduced primary structure yields a protein of 117.4 kDa. Because this protein contains RNA helicase consensus motifs, among them a "DEAD" box, we have termed it HEL117 (for helicase of 117.4 kDa). Besides the helicase consensus motifs, HEL117 contains an arginine-serine (RS)-rich domain, which occurs in some proteins involved in RNA splicing. Moreover, the COOH-terminal region of 78 residues of HEL117 is 38.5% identical and 59% similar to the COOH-terminal region of a yeast PRP5 protein that is involved in RNA splicing. Rabbit antibodies generated against a synthetic peptide of HEL117 identified a single polypeptide not only in rat cells but also in cells of other mammals as well as chicken. The antibodies revealed a finely punctate and speckled intranuclear staining in immunofluorescence microscopy. A monoclonal antibody against a human splicing factor containing an RS domain (SC35) showed, in double immunofluorescence microscopy, largely overlapping staining consistent with HEL117 being involved in RNA splicing.