Role of the RNA recognition motif of the E1B 55kDa protein in the adenovirus type 5 infectious cycle

Although the adenovirus type 5 (Ad5) E1B 55kDa protein can bind to RNA in vitro, no UV-light-induced crosslinking of this E1B protein to RNA could be detected in infected cells, under conditions in which RNA binding by a known viral RNA-binding protein (the L4 100kDa protein) was observed readily. Substitution mutations, including substitutions reported to inhibit RNA binding in vitro, did not impair synthesis of viral early or late proteins or alter significantly the efficiency of viral replication in transformed or normal human cells. However, substitutions of conserved residues in the C-terminal segment of an RNA recognition motif specifically inhibited degradation of Mre11. We conclude that, if the E1B 55kDa protein binds to RNA in infected cells in the same manner as in in vitro assays, this activity is not required for such well established functions as induction of selective export of viral late mRNAs.