The C proteins of heterogeneous nuclear ribonucleoprotein complexes interact with RNA sequences downstream of polyadenylation cleavage sites.

The heterogeneous nuclear ribonucleoprotein C1 and C2 proteins were preferentially cross-linked by treatment with UV light in nuclear extracts to RNAs containing six different polyadenylation signals. The domain required for the interaction was located downstream of the poly(A) cleavage site, since deletion of this segment from several polyadenylation substrate RNAs greatly reduced cross-linking efficiency. In addition, RNAs containing only downstream sequences were efficiently cross-linked to C proteins, while fully processed, polyadenylated RNAs were not. Analysis of mutated variants of the simian virus 40 late polyadenylation signal showed that uridylate-rich sequences located in the region between 30 and 55 nucleotides downstream of the cleavage site were required for efficient cross-linking of C proteins. This downstream domain of the simian virus 40 late poly(A) addition signal has been shown to influence the efficiency of the polyadenylation reaction. However, there was not a strict correlation between cross-linking of C proteins and the efficiency of polyadenylation.