Encapsidation of adenovirus 16 DNA is directed by a small DNA sequence at the left end of the genome

Abstract

We have identified a DNA sequence in adenovirus type 16 which contains recognition signals for encapsidation of the viral DNA. The sequence acts in cis to direct the encapsidation of DNA from the end of the viral genome where it is located. The sequence is normally contained in the first 390–400 bp of the left end of the genome. The location was determined by analyzing a series of spontaneous mutants of Ad16 which carried reduplications of 200 to >500 bp of left end sequences at the right end of the genome, thus giving rise to enlarged inverted terminal repetitions (ITR). In plaque-purified (PP) Ad16 prototype virus the subgenomic DNA found in incomplete virus particles exclusively represents left end sequences. When the reduplication mutants were analyzed, we found that a reduplication of about 390 bp enabled subgenomic DNA molecules containing the right end to be encapsidated into incomplete particles as well. A reduplication of about 290 bp, however, did not allow subgenomic DNA containing the right end to be encapsidated. The difference in encapsidation described could not be attributed to an asymetric DNA replication in the mutants, since subgenomic DNA originating from both ends of the genome was produced in equal amounts in the infected cells. We conclude that an essential part of the encapsidation sequence must be located between 290 and 390 bp from the left end of the Ad16 genome.