TRANS MESSENGER-RNA SPLICING IN TRYPANOSOMES - CLONING AND ANALYSIS OF A PRP8-HOMOLOGOUS GENE FROM TRYPANOSOMA-BRUCEI PROVIDES EVIDENCE FORA U5-ANALOGOUS RNP

In trypanosomes all mRNAs are generated through trans mRNA splicing, r equiring the functions of the small nuclear RNAs U2, U4 and U6. In the absence of conventional cis mRNA splicing, the structure and function of a US-analogous snRNP in trypanosomes has remained an open question . In cis splicing, a U5 snRNP-specific protein component called PRP8 i n yeast and p220 in man is a highly conserved, essential splicing fact or involved in splice-site recognition and selection, We have cloned a nd sequenced a genomic region from Trypanosoma brucei, that contains a PRP8/p220-homologous gene (p277) coding for a 277 kDa protein. Using an antibody against a C-terminal region of the trypanosomal p277 prote in, a smalI RNA of similar to 65 nucleotides could be specifically co- immunoprecipitated that appears to be identical with a US RNA (SLA2 RN A) recently identified by Dungan et al, (1996), Based on sedimentation , immunoprecipitation and Western blot analyses we conclude that this RNA is part of a stable ribonucleoprotein (RNP) complex and associated not only with the p277 protein, but also with the common proteins pre sent in the other trans-spliceosomal snRNPs. Together these results de monstrate that a US-analogous RNP exists in trypanosomes and suggest t hat basic functions of the US snRNP are conserved between cis and tran s splicing.