The Schizosaccharomyces pombe proteins that bind to the human HnRNPA1 winner RNA

Although extensively characterized in human cells, no heterogeneous nuclear ribonucleoprotein (hnRNP) has been found in the fission yeast Schizosaccharomyces pombe which is amenable to genetic studies and more similar to mammals than Saccharomyces cerevisiae is in terms of RNA processing. As a first step to characterize hnRNPs from S. pombe, attempt was made to find human hnRNP A1 homologs from S. pombe. The RNA molecule (A1 winner) containing the consensus high-affinity hnRNP A1 binding site (UAGGGA/U) was synthesized in vitro and used in an ultravilolet (UV) light-induced protein-RNA cross-linking assay. A number of S. pombe proteins bound to the A1 winner RNA. An approximately 50-kDa protein (p50) crosslinked more efficiently to the A1 winner RNA than other proteins. The p50 protein did not crosslink to a nonspecific RNA, but rather to the A1-5′SS RNA in which the consensus 5′ splice junction sites of S. pombe introns were abolished. This suggests that the p50 protein binds specifically to the consensus high affinity hnRNP A1 binding site. The p50 protein, however, did not bind to the single-stranded DNA to which the human hnRNP A1 could bind and be eluted with 0. 5 M NaCl. Further analysis should reveal more features of this RNA-binding protein.