Characterization of a temperature-sensitive mutant of human adenovirus type 7.

The properties of a naturally occurring temperature-sensitive (ts) mutant of human adenovirus type 7 (Ad7) were studied. Mutant Ad7 (19), or E46-, was the nonhybrid adenovirus component derived from the defective simian virus 40 (SV40)-Ad7 hybrid (PARA). Growth of the mutant was restricted at 40.5 degrees C, and the ratios of virus yields in KB cells at 40.5 and 33 degrees C were 10(-2) to 10(-3). Viral DNA synthesis and the synthesis of adenovirus-specific antigens (tumor, capsid, hexon, and penton antigens) appeared normal at the restrictive temperature. The assembly of virus particles was aberrant, as determined by thin-section of infected cells. The infectivity of mutant virions was heat labile at 50 degrees C, suggesting a ts defect in a structural component of the viron. Analysis by polyacrylamide gel electrophoresis of [35S]methionine-labeled polypeptides synthesized in mutant-infected cells suggested that at least the major virion polypeptides were synthesized at the restrictive temperature. A lack of inhibition of host protein synthesis late in mutant infections, as compared with wild-type (WT) infections at both the permissive and nonpermissive temperatures, made quantitation of infected-cell polypeptides difficult. Analysis of the assembly of capsomeres from cytoplasmic extracts of infected cells on sucrose gradients and by non-dissociating polyacrylamide gel electrophoresis suggested that hexon capsomeres were made at 40.5 degrees C. The hexon capsomeres made by the mutant at either 33 or 40.5 degrees C displayed a decreased migration in the non-dissociating gels compared with the WT hexon capsomeres. The molecular weights of the mutant and WT hexon polypeptides were identical. These results suggest that the ts lesion of this group B human Ad7 mutant may be reflected in altered hexons. The mutant Ad7 interfered with the replication of adenovirus types 2 and 21 at the elevated temperature.