The C-terminal region of hPrp8 interacts with the conserved GU dinucleotide at the 5 ' splice site

A U5 snRNP protein, hPrp8, forms a UV-induced crosslink with the 5' splice site (5'SS) RNA within splicing complex B assembled in trans- as well as in cis-splicing reactions. Both yeast and human Prp8 interact with the 5'SS, branch site, polypyrimidine tract, and 3'SS during splicing. To begin to de fine functional domains in Prp8 we have mapped the site of the 5'SS crossli nk within the hPrp8 protein. Immunoprecipitation analysis limited the site of crosslink to the C-terminal 50-60-kDa segment of hPrp8. In addition, siz e comparison of the crosslink-containing peptides generated with different proteolytic reagents with the pattern of fragments predicted from the hPrp8 sequence allowed for mapping of the crosslink to a stretch of five amino a cids in the C-terminal portion of hPrp8 (positions 1894-1898). The site of the 5'SS:hPrp8 crosslink falls within a segment spanning the previously def ined polypyrimidine tract recognition domain in yPrp8, suggesting that an o verlapping region of Prp8 may be involved both in the 5'SS and polypyrimidi ne tract recognition events. In the context of other known interactions of Prp8, these results suggest that this protein may participate in formation of the catalytic center of the spliceosome.