Low pH RNA-protein interactions in turnip yellow mosaic virus

It has been previously shown that turnip yellow mosaic virus capsids and RNA obtained by incubation in 8 M urea, 1 M NaCl at pH 7 could be reassociated by dialysis against low ionic strength buffer, in the presence of MgCl 2 or spermidine. The nucleoprotein complexes differed from native virions in stability at neutral pH and in RNase-resistance at low pH, but the association is specific, as TMV-RNA or alfalfa mosaic virus-RNA was found not to interact with capsids under such conditions. We present here further data concerning the specificity of this interaction. Radioactive poly(A), poly(C), poly(G) and poly(U) were added to the dissociation mixture of TYMV in the presence of 5 × 10 −3 M MgCl 2 . It was found that only poly C reassociated specifically with “nascent capsids.” Poly(A) did not interact at all with either capsids or RNA. At either neutral or acidic pH, small amounts of poly U bound to capsids, but not to RNA or virions. Poly(G) forms a hybrid with TYMV-RNA. The nature of low pH RNA-protein interaction in TYMV is discussed.