Genetic complementation in the Xenopus oocyte: co-expression of sea urchin histone and U7 RNAs restores 3' processing of H3 pre-mRNA in the oocyte.

Efficient 3' processing of sea urchin histone H3 pre-mRNA in the Xenopus oocyte is dependent on co-injection of sea urchin U7 RNA or U7 RNP. We show that U7 RNP is a genuine member of the (Sm-type) U-snRNP family as judged by immunoprecipitation of the U7 RNA and U7 RNPs with polyclonal anti-trimethylguanosine and monoclonal anti-Sm antibodies. Sea urchin U7 RNA can be produced in the frog oocyte from RNA genes driven by a Xenopus U2 promoter. The transcripts thus synthesized have all the known characteristics of authentic U7 RNA. Our experiments further suggest that sequences near the 5' end of the U7 RNA mediate Sm-immunoprecipitability. Co-expression of sea urchin U7 RNA gene and H3 histone gene sequences in the frog oocyte complements faulty 3' maturation of histone pre-mRNA. This provides irrefutable evidence that the sea urchin U7 RNA identified earlier is indeed an essential component of the 3' processing of histone mRNAs.