Adenovirus early region 4 is required for efficient virus particle assembly.

H2dl807, a defective deletion mutant of human adenovirus type 2 lacking parts of early regions 3 and 4 and all of late region 5, was severely defective for virus particle assembly on HeLa cells, producing about 1% of the normal yield of particles. On Vero cells, H2dl807 produced only 5% as many particles as wild type, while on W162 cells, a Vero cell derivative which supports the growth of early region 4 mutants, H2dl807 produced nearly 40% of the wild-type level of particles. Two other defective deletion mutants, H2dl802 and H5dl1021, which lack parts of early region 3 and which are incapable of making fiber, the product of late region 5, were wild type for virus assembly. These data suggest that the cause of the assembly defect of H2dl807 is the lack of a diffusible early region 4 product. H2dl807-infected Vero cells accumulated nearly wild-type amounts of viral late proteins in the nucleus and cytoplasm. Thus, the defect of the mutant in assembly on Vero cells is not due to a general lack of late proteins. Finally, the fact that H2dl802 and H5dl1021 make wild-type amounts of virus particles suggests that fiber is not essential for adenovirus assembly.