Abstract
The hamster cell line CLAC1 originated from a tumor induced by injecting human adenovirus type 12 (Ad12) into newborn hamsters. Each cell contained about 12 copies of viral DNA colinearly integrated at two or three different sites. We have cloned and sequenced a DNA fragment comprising the site of junction between the left terminus of Ad12 DNA and cellular DNA. The first 174 nucleotides of Ad12 DNA were deleted at the site of junction. Within 40 nucleotides, there were one tri-, two tetra-, one penta-, and one heptanucleotide which were identical in the 174 deleted viral nucleotides and the cellular sequence replacing them. In addition, there were patch-type homologies ranging from octa- to decanucleotides between viral and cellular sequences. There is no evidence for a model assuming adenovirus DNA to integrate at identical cellular sites. The cellular DNA sequence corresponding to the junction fragment was cloned also from BHK21 (B3) hamster cells and sequenced. Up to the site of linkage with viral DNA, this middle repetitive cellular DNA sequence was almost identical with the equivalent sequence from CLAC1 hamster cells. Taken together with the results of previously published analyses (11, 12), the data suggest a model of viral (foreign) DNA integration by multiple short sequence homologies. Multiple sets of short patch homologies might be recognized as patterns in independent integration events. The model also accounts for the loss of terminal viral DNA sequences.