ROLE OF THE MU-1 PROTEIN IN REOVIRUS STABILITY AND CAPACITY TO CAUSE CHROMIUM RELEASE FROM HOST-CELLS

The reovirus M2 gene is associated with the capacity of type 3 strain Abney (T3A) intermediate subviral particles (ISVPs) to permeabilize ce ll membranes as measured by chromium (Cr-51) release (P. Lucia-Jandris , J. W. Hooper, and B. N. Fields, J. Virol, 67:5339-5345, 1993). In ad dition, reovirus mutants with lesions in the M2 gene can be selected b y heating virus at 37 degrees C for 20 min in 33% ethanol (D. R. Wessn er and B. N. Fields, J. Virol. 67:2442-2447, 1993). In this report we investigated the mechanism by which the reovirus M2 gene product (the mu 1 protein) influences the capacity of reovirus ISVPs to permeabiliz e membranes, using ethanol-selected T3A mutants. Each of three T3A eth anol-resistant mutants isolated (JH2, JH3, and JH4) exhibited a decrea sed capacity to cause Cr-51 release relative to that of wild-type T3A. Sequence analysis of the M2 genes of mild-type T3A and the T3A mutant s indicated that each mutant possesses a single amino acid substitutio n in a central region of the 708-amino-acid mu 1 protein: JH2 (residue 466, Tyr to Cys), JH3 (residue 459, Lys to Glu), and JH4 (residue 497 Pro to Ser), Assays performed with reovirus natural isolates, reassor tants, and a set of previously characterized type 3 strain Dearing (T3 D) ethanol-resistant mutants revealed a strong correlation between eth anol sensitivity and the capacity to cause Cr-51 release, We found tha t ISVPs generated from the T3A and T3D mutants were stable when heated to 50 degrees C, whereas wild-type T3A ISVPs are inactivated under th ese conditions, Together, these data suggest that amino acid substitut ions in a central region of the mu 1 protein affect the capacity of th e ISVP to permeabilize L-cell membranes by altering the stability of t he virus particle.