BINDING-PROPERTIES OF NEWLY IDENTIFIED XENOPUS PROTEINS CONTAINING DSRNA-BINDING MOTIFS

Background: Although most RNA-binding proteins recognize a complex set of structural motifs in their RNA target, the double-stranded (ds)RNA -binding proteins are limited to interactions with double helices. Rec ently, it has been discovered that some dsRNA-binding proteins share r egions of amino-acid similarity known as dsRNA-binding motifs. Results : A Xenopus ovary cDNA. expression library was screened with radiolabe led dsRNA to identify previously uncharacterized dsRNA-binding protein s. The analysis of an incomplete cDNA identified during the screen led to the discovery of two longer cDNAs of related sequence. The protein s encoded by these cDNAs each contained two dsRNA-binding motifs, in a ddition to an auxiliary domain rich in arginine and glycine. The nucle ic-acid-binding properties of a fusion protein containing the two dsRN A-binding motifs and the auxiliary domain were analyzed using a gel mo bility shift assay. The fusion protein bound dsRNA of a variety of dif ferent sequences, and exhibited a preference for binding to dsRNA and RNA-DNA hybrids over other nucleic acids. Appropriate mRNAs, correspon ding to each cDNA, were detected in polyadenylated RNA isolated from X enopus stage VI oocytes, but translation of one of the mRNAs appeared to be masked until meiotic maturation. Conclusion: dsRNA-binding motif s are often found in proteins that bind dsRNA, and our results show th at they can be associated with auxiliary domains rich in arginine and glycine. These motifs can confer very tight binding to dsRNA. Binding can also occur to RNA-DNA hybrids, suggesting recognition of some aspe ct of the A-form helical structure that is adopted by both dsRNA and R NA-DNA hybrids.