Adenovirus L1 52- and 55-kilodalton proteins are required for assembly of virions

A variant of adenovirus type 5 that contained a mutation within the L1 52- and 55-kilodalton (52/55K) protein-coding region was isolated. The mutant, termed ts369, produced L1 52/55K proteins with a two-amino-acid substitution and was temperature sensitive. Temperature-shift experiments indicated that the ts369 defect was late in the viral growth cycle. DNA replication and synthesis of late proteins occurred normally in ts369-infected cells at the nonpermissive temperature, but mature virions were not produced. Rather, capsidlike particles associated with the left-terminal region of the viral chromosome accumulated. These incomplete particles could not be chased into mature virions when the infected cells were shifted to the permissive temperature. However, previously synthesized proteins could be assembled into virions in the presence of a protein synthesis inhibitor upon shiftdown from the nonpermissive temperature, suggesting that the inactivation of the L1 52/55K proteins was reversible. These results indicate that the adenovirus L1 52/55K proteins play a role in the assembly of infectious virus particles.