The M1 gene is associated with differences in the temperature optimum of the transcriptase activity in reovirus core particles.

The reovirus core is a multienzyme complex that contains five different structural proteins and 10 segments of double-stranded RNA. The core is responsible for transcribing mRNA from the enclosed double-stranded RNA. The reovirus transcriptase has an unusual temperature profile, with optimum transcription occurring at approximately 50 degrees C and little activity occurring below 30 or above 60 degrees C. Purified reovirus serotype 1 Lang (T1L) cores transcribed most efficiently at 48 degrees C. The transcriptase temperature optimum of purified reovirus serotype 3 Dearing (T3D) cores was 52 degrees C. In addition, T1L cores produced more mRNA per particle than did T3D cores at their respective temperature optima. Core particles were purified from T1L x T3D reassortants and were used to map these differences. The M1 gene, which encodes minor core protein mu 2, was uniquely associated with the difference in temperature optimum of transcription (P = 0.0003). The L1 gene, which encodes minor core protein lambda 3 (previously implicated as the RNA polymerase), and the M1 gene were associated with the difference in absolute amounts of transcript produced (P = 0.01 and P = 0.0002, respectively). These data suggest that minor core protein mu 2 also plays a role in reovirus transcription.