An unusual symmetric recombinant between adenovirus type 12 DNA and human cell DNA

Abstract

On purification of human adenovirus type 12 (Ad12) by equilibrium sedimentation in CsCl density gradients, 2 bands of particles, Ad12-3 and Ad12-3a, are observed. The particles from band Ad12-3a contain a recombinant of human host cell DNA and of Ad12 DNA. The human cell DNA sequences contain repetitive DNA recurring 200-500 times in cellular DNA. Ad12 DNA and the recombinant genomes exhibit the same or similar lengths. A constant amount of DNA is apparently packaged into complete Ad12 particles. On cleavage of KB (oral epidermoid carcinoma) cellular DNA with EcoRI BamHI, HinfI, Msp I, Mbo I, Pst I or Bgl II, the 32P-labeled cellular DNA from Ad12-3a particles hybridizes on Southern blots to distinct bands of KB DNA. There is also less specific background hybridization that is not observed in the control. The cellular DNA from Ad12-3a particles is not methylated, whereas the same cellular sequences in KB cell DNA appear to be extensively methylated. On denaturation and renaturation, the recombinant DNA molecules are converted to molecules half as long as Ad12 DNA, as determined by gel electrophoresis and EM. The recombinant DNA molecules were terminally labeled by exonuclease III treatment and subsequent refilling of the depleted segments with [32P]dNTP (deoxyribonucleoside triphosphate) by using DNA polymerase I (Klenow fragment). When these molecules were cleaved with EcoRI, BamHI, Msp I or Pst I, only 1 terminal DNA fragment was labeled. The results of partial digestion experiments using Msp I, HinfI or Mbo I are consistent with a model in which 700-1150 base pairs from the left terminus of Ad12 DNA are linked to host cell DNA containing repetitious sequences, and this structure is symmetrically duplicated as a large inverted repeat of the type ABCDD''C''B''A''. The Ad12 DNA sequences flank the entire molecule, which consists mainly of human KB cell DNA. The recombinants appear to be stable on serial passage of the virus preparation for many years, although variations in the sequence of the recombinants occur. These symmetric recombinant (SYREC) molecules suggest a way to use adenovirus DNA as a eukaryotic vector. Their occurrence provides further evidence for the generation of virus-host DNA recombinants and may help elucidate the role this interaction may have in adenovirus replication and oncogenesis.