Gene expression, viral material

Ribosomes phosphorylated vitro show no alteration in their translational activity (5, ) Trivial explanations such as the possibility that the ribosomes are dephosphorylated in the translation assay seem to have been eliminated. It is, of course, possible that current assay methods are inadequate to detect subtle changes caused by phosphorylation, but it is equally valid to draw the strai tforward conclusion that phosphorylation does not affect the activity of ribosomes. This is in accord with the fact that changes in the phosphorylation state of ribosomes vivo do not appear to correlate with alterations in the efficiency of the ribosomes in protein biosynthesis. The one possible exception is the phosphorylation of one of the small ribosomal subunit proteins (S2) that occurs after infection by vaccinia virus (8). The timing of the phosphorylation of S2 seems however to be related neither to the shut-off of host cell protein synthesis nor to the switch from early viral protein synthesis to late gene expression, and it remains to be proven whether the phosphorylation has any material effect on ribosome activity or specificity. 

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