Replication of chimeric tobacco mosaic viruses which carry heterologous combinations of replicase genes and 3' noncoding regions.

Three tobacco mosaic virus (TMV)-L (tomato strain)-derived chimeras, designated OL1, LG11, or LK31, were constructed by replacing the 3' noncoding region with the corresponding sequence of TMV-OM (common strain), cucumber green mottle mosaic virus (CGMMV), or TMV-Cc (cowpea strain), respectively. The genomic RNAs of TMV-L, -OM, and CGMMV carry histidine-accepting tRNA-like structures at their 3' termini, while the genome of TMV-Cc accepts valine. The three chimeric viruses were able to multiply in both tobacco protoplasts and plants. Multiplication of OL1 in protoplasts was similar to that of the parental strain, L, but in the cases of LG11 and LK31 multiplication was decreased. Sequence analyses of progeny RNAs revealed that viruses with chimeric sequences propagated. These data suggested that TMV-L replicase recognizes the 3' terminal structures of TMV-OM, CGMMV, and TMV-Cc and can initiate minus-strand RNA synthesis. The relationship between the virus-coded component(s) of TMV replicase and the 3' terminal region may not be so stringent.