Reovirus serotypes 1 and 3 differ in their in vitro association with microtubules

Abstract

Utilizing negative-stain EM in which similar concentrations of reovirus types 1 and 3 were incubated with a C support film containing chick brain, rabbit brain or [human cervical carcinoma] HeLa cell microtubules, 81% of type 1 and 56% of type 3 exhibited an association with the apparent edge of the microtubule. There may be a high level of specific affinity for type 1 but not for type 3 to microtubules, since it was previously determined that only 50% of randomly associated particles would be associated with the edge. The high edge binding of reovirus type 1 is virtually independent of the origin of microtubule, or of whether microtubules or virus was initially adhered to the support film. Reovirus type 1-specific antiserum reduced the edge binding of reovirus type 1 to 45%, whereas type 3-specific antiserum caused no loss (within the variability of the assay) of the edge binding of reovirus type 1 to microtubules (76% edge bound). High edge binding of reovirus type 1 to microtubules was correlated with the presence of type 1 .sigma.1 polypeptide. This minor outer capsid polypeptide was encoded in the S1 double-stranded RNA segment and was the viral hemagglutinin and neutralization antigen. Recombinant reovirus clones containing the S1 double-stranded RNA segment of type 1 (80 and 802) showed about 85% edge binding, as compared to a value of 42% for clones with the S1 gene of type 3 (204). EM of purified reovirus types 1 and 3 by negative staining revealed that type 1 and 802 capsomers were distinctly visualized, but those of type 3 and 204 appeared diffuse. Thus, the greater in vitro binding of type 1 to microtubules may reflect an increased accessibility of certain of its outer capsomers, and thereby, .sigma.1 polypeptides to microtubules. Examination of thin sections of reovirus type 1- and 3-infected cells at 24-48 h postinfection at 31.degree. C showed that about 8 times as many viral factories in type 1-infected cells exhibited an extensive association of virus particles with microtubules, as compared to viral factories of type 3-infected cells. Thus, both in vivo and in vitro there appears to be a greater specificity for the association of reovirus type 1 particles with microtubules, as compared to reovirus type 3 particles.