The inability of the Psammechinus miliaris H3 RNA to be processed in the Xenopus oocyte is associated with sequences distinct from those highly conserved amongst sea urchin histone RNAs.

3' processing of precursors of the H3 RNA of the sea urchin Psammechinus miliaris in Xenopus oocytes is dependent upon sea urchin U7 snRNA. Sequences necessary for this interaction are highly conserved in all sea urchin histone precursor RNAs (including the Psammechinus H3) which, in contrast, are efficiently processed in the Xenopus oocyte without the addition of the homologous U7 snRNA. We resolve this seeming paradox by demonstrating here that the inability of the sea urchin Psammechinus miliaris H3 histone RNA to be processed in the Xenopus oocyte is associated with nucleotides immediately 3' to the conserved downstream sea urchin histone sequence element. Thus, a sequence-specific element (or lack of it) is responsible for the poor recognition of the Psammechinus H3 precursor RNA by the Xenopus processing machinery.