Anti-sense regions in satellite RNA of cucumber mosaic virus form stable complexes with the viral coat protein gene.

The interaction in vitro of the RNA of the Q-strain of cucumber mosaic virus (CMV) with its satellite RNA (sat-RNA) has been studied. In hybridisation reactions containing 30% formamide at 45 degrees, sat-RNA binds to CMV RNA 3 and 4 but not to CMV RNA 1 and 2 or RNA from tobacco mosaic virus and alfalfa mosaic virus. The viral coat protein gene present in RNA 3 and 4 contains the site of binding but this region does not contain complementary sequences of any significant length to the sat-RNA sequence. However, the optimum alignment of short complementary sequences present in these regions revealed a stable structure in which it is proposed that sat-RNA twists around the coat protein gene so that two separate blocks of nucleotides in sat-RNA base pair in opposite directions with two adjacent blocks in the coat protein gene to form a knot-like structure. The binding site is a region of 33 nucleotides within the coding region of the coat protein gene which base pairs with residues 98-113 and 134-152 of sat-RNA. The possibility of the binding region of sat-RNA functioning as an "anti-sense" sequence in regulation of the viral coat protein synthesis is discussed.