Specificity of RNA and coat protein interaction in alfalfa mosaic virus and related viruses

Well-defined coat protein binding sites were found to be present on the genomic RNAs of AlMV and TSV. In view of the regulatory importance of these sites in virus multiplication, the possibility that nonrelated proteins also were able to interact with these sites was investigated. The coat proteins of TSV, BMV, CMV, and SBMV recognize specific sites on AlMV RNA 1. The significance of these sites in virus multiplication is discussed. No specific binding sites were found with TMV coat protein or the nonviral proteins ovalbumin, myoglobin, and lysozyme. Moreover, the ability of AlMV coat protein to recognize specific sites on the heterologous RNAs of TSV, BMV, bacteriophage MS2, and Escherichia coli was tested. No specific sites were found with MS2-RNA. However, specific binding sites were found with BMV-RNA 3 and, unexpectedly, with E. coli 16 S ribosomal RNA. From these data it was concluded that binding of AlMV and TSV coat proteins to their genomic RNAs is a specific process. However, the binding of coat protein to BMV-RNAs and to ribosomal RNAs may result from secondary folding that may have been conserved for other purposes throughout evolution of the RNAs.