A Unique Form of Terminal Redundancy in Adenovirus DNA Molecules

A unique form of terminal redundancy has been observed in DNA molecules extracted from several human adenovirus serotypes. Electron microscopic studies reveal that single-stranded circular molecules are formed when native DNA is denatured and then annealed. Temperatures approaching the T(m) of native DNA are required to convert circles to linear molecules, indicating a high degree of self-complementarity between terminal base sequences of DNA strands. Single-stranded circles are not generated if a limited number of nucleotides (2-4%) are removed from the 3' ends of native DNA by digestion with Escherichia coli exonuclease III before denaturation and annealing. The lenght of the redundant segment appears to differ among major serotypic groups, and a possible association between increased length of the redundant segment and increased oncogenic capability of virus serotype is suggested. Evidence for the configuration of the duplex closure region of circular molecules is also presented.