Mapping of the two coat protein genes on the middle RNA component of squash mosaic virus (comovirus group)

Squash mosaic virus, a member of the comovirus group, has a divided genome identified as middle-component RNA (M RNA; MW = 1.4 x 10(6)) and bottom-component RNA (B RNA; MW = 2 x 108). The isometric capsid of squash mosaic virus is composed of two distinct protein monomers with molecular weights of 22,000 (22k) and 42k. The isolated RNA components were translated in a rabbit reticulocyte lysate system. Translation products of the B RNA had estimated molecular weights of 190k, 51k, and 32k, while the M RNA products ranged in estimated molecular weight from 22k to 112k. Products of the B RNA did not react with antisera prepared to the 22k and 42k coat proteins. All of the M RNA products reacted with antiserum to the 22k coat protein and all the products larger than 35k reacted with antiserum to the 42k coat protein. The 22k product of M RNA translation had a V-8 protease peptide pattern identical to that of the 22k coat protein. Protease peptide patterns of the M RNA 64k and 112k-105k translation products showed a number of peptide fragments similar to those produced by the 22k and 42k coat proteins, indicating that the translation products contained the sequences of the two coat proteins. The proposed gene order of translation for squash mosaic virus M RNA is as follows: 5' end-22k coat protein gene-42k coat protein gene-48k unidentified protein gene-untranslated sequence-3' end.