Base-pair formation between noncapped influenza virus in vitro transcripts and 18S rRNA in rabbit reticulocyte 80S ribosome-mRNA complexes detected by psoralen photoreaction.

RNA-RNA interactions between 18S ribosomal RNA and noncapped influenza cRNA were detected by psoralen photochemical cross-linking in reticulocyte 80S ribosome-cRNA complexes. In vitro transcripts of type A influenza virus synthesized by endogenous RNA polymerase with adenylyl-(3'----5')-guanosine primer formed 80S complexes with rabbit reticulocyte ribosomes. The extent of the complex formation by these noncapped cRNAs was less than that by the m7G-capped reovirus in vitro transcripts, but the former RNAs in the 80S complexes were cross-linked to 18S rRNA as efficiently as the latter RNAs by photoreaction with an RNA cross-linking agent, 4'-aminomethyl-4,5',8-trimethylpsoralen. These results suggested that mRNA with or without the cap structure on the 5'-terminal can form complexes with the ribosomes in a eukaryotic cell-free translation system by base-pair formation with 18S rRNA. Correspondingly, sequences capable of forming extensive base-pairs including four- to five-base complementarities were found between the 3'-terminal of rabbit reticulocyte 18S ribosomal RNA and the 5'-noncoding regions of either influenza virus transcripts or reovirus mRNA.