Incomplete particles of canine adenovirus type 1: occurrence and structure

Replication of canine adenovirus (CAV) type 1 in dog kidney (DK) cells has been found to generate particles containing double-stranded DNA molecules of size 6-9 kbp with protein moieties at their 5' termini. The particles formed a discrete band in CsCl gradients at a density intermediate to that of intact virions and empty capsids. Electron microscopy demonstrated that they were morphologically similar to intact virions. Restriction enzyme digests and hybridization experiments revealed the existence of DNA molecules consisting of sequences extending from left and right termini of the intact genome. The subgenomic DNAs, therefore, appear to be viral DNA with the majority (24-26 kbp) of its internal sequences deleted. Agarose gels of viral DNA isolated from DK cells infected with plaque-purified CAV revealed, in addition to the intact viral genome, one or more sharp, well-defined subgenomic DNA bands, the sizes of which varied from approximately 6 to 9 kbp among individual isolates. Incomplete particles of this sort were found in the two strains of CAV type 1 tested (Connaught ICHV and Glaxo), but not in a strain of CAV type 2 (Manhattan).