Human U1 snRNP-specific C protein: complete cDNA and protein sequence and identification of a multigene family in mammals.

A complementary DNA clone for the human U1 snRNP-specific C protein has been isolated. The nucleotide sequence of the 733 bp cDNA insert includes a 15 bp 5'-untranslated region, an open reading frame of 477 bp corresponding to 159 amino acids (Mr = 17,373 D), and a 223 bp 3'-untranslated region. The identity of the clone was confirmed by in vitro translation of hybrid-selected mRNA or an RNA transcript synthesized from the cDNA. The in vitro synthesized C protein has a slightly greater mobility on SDS-polyacrylamide gels, indicating that the in vivo product is post-translationally modified. The deduced primary structure contains a segment of high proline and methionine content. A region homologous to the RNP consensus sequence, found in the other two U1 snRNP-specific proteins 70K and A, is absent. Analysis of genomic DNA restriction enzyme digests shows hybridizing fragments in the genome of all vertebrate classes. The results are consistent with multi-copy representation of the C protein gene in mammals, whereas in the other vertebrate classes the related protein seems to be encoded by a single-copy gene.