The reovirus mutant tsA279 has temperature-sensitive lesions in the M2 and L2 genes: the M2 gene is associated with decreased viral protein production and blockade in transmembrane transport.

Temperature-sensitive mutants provide an ideal means for dissecting viral assembly pathways. The morphological variants produced by and biological characteristics of tsA279, a previously uncharacterized mutant from the Fields' panel of temperature-sensitive mutants of reovirus, were determined under restrictive growth conditions. The mutant showed a distinctive pattern of increased temperature sensitivity as the temperature was raised from 39 degrees to 40 degrees. Wild-type reovirus type 1 Lang and the mutant were crossed to generate reassortants. Efficiency of plating analyses of the reassortants showed that tsA279 has temperature-sensitive lesions in two genes, a mildly temperature-sensitive one in L2, which encodes core spike protein lambda 2, and a stronger, dominant lesion in M2, which encodes major outer capsid protein mu 1. Electron microscopic examination of thin-sectioned tsA279-infected cells showed three ways in which the mutant phenotypes were expressed. The mutant appeared to be blocked in transmembrane transport of virions, a phenotype that mapped to the M2 gene; the mutant produced significantly reduced amounts of identifiable particles; and those particles that were produced appeared to be morphological variants. Immunofluorescent microscopy and immunoprecipitations of tsA279- and various T1L x tsA279 reassortant-infected cells suggested that the reduction in observed progeny was caused by a decreased production of viral proteins at the nonpermissive temperature. This phenotype also mapped to the mutant M2 gene.