Translational discrimination between the four RNAs of alfalfa mosaic virus

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Abstract
In an attempt to relate the translational characteristics of alfalfa mosaic virus (A1MV) RNA to their structure, the relative affinities (discrimination ratios) of these RNA for the initiation complex were measured in the wheat germ extract and in the nuclease-treated reticulocyte lysate using a competition method designed by Brendler et al. Previously, it was found that the MW distribution of the translation products was independent of RNA concentration in both translation systems. In the wheat germ extract the discrimination ratios are very similar for 2 strains of A1MV (S and B) which differ mainly by the presence (strain S) or absence (strain B) of a stable 5''-proximal hairpin. Thus, this structure has no bearing on discrimination. Taking the affinity of RNA 3 as reference, the following orders of magnitude are found for the affinities of the different RNA in the wheat germ: RNA 3, 1.0; RNA 1, 10; RNA 2, 60; RNA 4, 150. In the reticulocyte lysate the discrimination ratios are not significantly different from the wheat germ. Thus, the mechanism of discrimination is probably essentially the same in the 2 translation systems, despite a difference in rate-limitation.