Near identity of 3- RNA secondary structure in bromoviruses and cucumber mosaic virus.

The 3- terminal sequences of RNAs 1, 2, 3 and 4 from each of the three bromoviruses (brome mosaic, cowpea chlorotic mottle and broad bean mottle viruses) and also from cucumber mosaic virus display interviral sequence similarity in addition to strong intraviral homology. Interviral similarity is much more evident when RNA secondary, rather than primary, structures are compared. The last 190 bases of the various RNAs can fold into strikingly similar, extensively base-paired secondary structures whose common features are supported by RNA structure mapping. The extreme 3' end of each viral RNA can base-pair in two distinct configurations. Bromovirus RNA 3s each contain an unusually accessible internal oligo(A) sequence which, in brome mosaic virus at least, is located in the intercistronic noncoding region. Functional implications of these structural features are discussed.