The origin of multiple polypeptides of molecular weight below 110 000 encoded by tobacco mosaic virus RNA in the messenger-dependent rabbit reticulocyte lysate

Abstract

Multiple polypeptides encoded by tobacco mosaic virus (TMV) RNA in the messenger-dependent rabbit reticulocyte lysate are not attributable to contaminating 3′-coterminal RNA fragments, multiple leaky termination codons or endonuclease activity opening-up legitimate or spurious internal initiation sites. Quantitative analysis of polypeptides encoded over a range of added RNA concentrations from 0.09 μg·ml −1 to 180 μg·ml −1 compared wi preparation, or with RNA extracted from the alkali-stable fraction of TMV suggest that apart from four legitimate virus-coded products of apparent M r approx. 165 000, 110 000, 30 000 and 17 500 all other polypeptides arise from the overlapping 5′-proximal cistrons either by (i) site-selective endonucleolytic cleavage, (ii) sense codon misreading, or (iii) specific regions of secondary structure on TMV RNA which impede ribosome translocation.