Generation of histone mRNA 3' ends by endonucleolytic cleavage of the pre-mRNA in a snRNP-dependent in vitro reaction

Incubation of SP6 generated mouse histone H4 mRNA precursors in nuclear extracts of HeLa cells yields processed mRNA species which end on the 3' adenosine of the conserved terminal ACCA sequence not unlike ten different histone mRNAs isolated from sea urchin embryos which end either on the 3' C or A. In the presence of 20 mM EDTA, the cleaved off 3' spacer portions of the RNA transcripts are readily detected, hence the 3' ends of histone mRNAs arise as a consequence of endonucleolytic cleavage(s) of the precursor RNA. The in vitro cleavage reaction is specifically inhibited by human antisera of the Sm-serotype, but not by control sera and can be rescued by the addition of a preparation of partially purified small nuclear RNPs to the antibody-depleted extract. Interestingly, the snRNP preparation is sufficient to elicit 3' processing of pre-mRNA in the absence of added nuclear extract.