Characterization of cloned measles virus mRNAs by in vitro transcription, translation, and immunoprecipitation.

A cDNA library was constructed from poly(A)+ RNA prepared from VERO cells infected with the Edmonston strain of measles virus. Clones corresponding to five major viral-specific transcripts were identified by northern blot hybridization analysis. Probes prepared from these five clones detected an additional five minor viral RNA transcripts. The sizes and hydridization patterns of these minor RNA species are consistent with their being bicistronic transcripts arising from a viral genomic template with the gene order 3'..NP-9/C-M-F-HA-(L)..5'. To assess the coding capacity of these cDNA clones they were inserted into pSP64, transcribed in vitro, the RNA was translated in reticulocyte lysates, and the protein was immunoprecipitated with specific antisera. From this analysis the genes for NP, P/C, M, F, and HA were identified. In vitro translation of natural mRNAs and SP6 transcripts of cDNAs consistently produced smaller polypeptides that appear to be initiated at internal AUGs. The relative abundance of these various cell-free translation products reflects the probability of translational initiation at the various in-frame AUGs. The patterns observed suggest that other factors besides sequences immediately flanking the AUGs have a significant effect on the selection of translational initiation sites. An increase in translational efficiency of the F transcript was achieved by removing 450 bases of the G-C-rich 5' noncoding region.