Two proteins crosslinked to RNA containing the adenovirus L3 poly(A) site require the AAUAAA sequence for binding.

The major proteins crosslinked by UV light to RNA containing the adenovirus-2 L3 poly(A) site are species of 155, 68 and 38 kd mol. wt (p155, p68 and p38). Mutation of AAUAAA to AAGAAA prevented cross-linking of the two larger proteins and destroyed the ability of the RNA to compete for binding of these proteins. However, association of p155 and p68 with precursor was unaffected by deletion of sequences downstream of the poly(A) site critical for in vitro polyadenylation. These two proteins are in the polyadenylation-specific, but not the nonspecific complexes detected by electrophoresis in nondenaturing gels. In addition, p155 and p68 are not found on RNA which has been processed. p155 bound a 15-nt oligomer containing AAUAAA, and thus does not require extended RNA sequence for interaction with RNA. Identified by immunoprecipitation with specific antibody, p38 is the C protein of heterogeneous ribonucleoprotein particles (hmRNPs). While p155 has an Sm epitope, it is not associated with snRNPs containing trimethylated guanosine caps.