Deletion of repeated sequences from tobacco mosaic virus mutants with two coat protein genes.

Tobacco mosaic virus (TMV) hybrids were constructed in vitro with an extra coat protein gene (gene order 5'- 126K/183K gene-30K gene-first coat protein gene-subgenomic mRNA promoter:second coat protein gene-3'). One coat protein gene was wild type and the other was derived from one of three coat protein mutants that elicit distinctive phenotypic responses. The hybrids contained large sequence repeats (up to 747 nucleotides). RNA transcripts of each of seven hybrid constructs initiated infections in host plants, but the progeny virus contained only one coat protein gene with no additional or missing nucleotides. Progeny of mutants with the two functional coat protein genes in different order within the genome retained coat protein gene sequence predicted by the number of repeated nucleotides 3' and 5' of the differential nucleotides. In contrast, progeny that resulted from virus hybrids with a wild-type and a nonfunctional coat protein gene possessed only the wild-type coat protein gene, even when the predicted progeny was a free-RNA virus. This demonstrated that selection strongly affected which progeny became predominant in the resulting populations.