The extent of binding of purified RSV(Pr-C) p19 and p12 to a variety of RNAs was measured using a sensitive nitrocellulose filter binding assay which is capable of detecting binding reactions with association constants as low as 3 × 106 liters × mol-1 (Hizi, A., Leis, J. P., and Joklik, W. K. 1977). RSV p19 bound 60 and 34 S RSV (Pr-C) RNA with association constants of 5.1 × 1011 and 1.8 × 1010 liters × mol-1. RSV p19 bound preferentially to specific double-stranded regions of the RNA since: (a) The association constant for Neurospora nuclease-digested 34 S RNA was the same as for untreated RNA; (b) the association constant for 34 S RNA partially digested with Escherichia coli RNase III (which is specific for double-stranded RNA regions) was 30-fold lower than for untreated RNA; (c) p19 prevented cleavage of 34 S RSV-RNA by E. coli RNase III; (d) p19 bound cell precursor RNAs containing RNase III-sensitive sites, but not mature RNAs lacking RNase III-sensitive sites. On the other hand, purified RSV p12 bound all RNAs tested with association constants roughly proportional to their molecular weights. A possible function for p19 in regulating the processing of viral RNA and its subsequent translation has been proposed.
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