Tobacco mosaic virus (TMV) encodes a 30-kDa movement protein (NIP) which en
ables viral movement from cell to cell. It is, however, unclear whether the
126- and 183-kDa replicase proteins are involved in the cell-to-cell movem
ent of TMV. In the course of our studies into TW-R, a strain with a host ra
nge different from that of TMV-U1, we have obtained an interesting chimeric
virus, UR-hel. The amino acid sequence differences between UR-hel and TMV-
U1 are located only in the helicase-like domain of the replicase. Interesti
ngly, UR-hel has a defect in its cell-to-cell movement. The replication of
UR-hel showed a level of replication of the genome, synthesis, and accumula
tion of MP similar to that observed in TMV-U1-inoculated protoplasts. Such
observations support the hypothesis that the replicase coding region may in
some fashion be involved in cell-to-cell movement of TMV.