THE STRUCTURE OF ADENOVIRUS-TYPE-12 DNA INTEGRATION SITES IN THE HAMSTER-CELL GENOME

Foreign DNA can integrate into the genomes of mammalian cells, and thi s process plays major roles in viral oncogenesis and in the generation of transgenic organisms and will be important in evolving regimens fo r human somatic gene therapy, In the present study, the insertion site s of adenovirus type 12 (Ad12) DNA genomes have been analyzed in detai l in the Ad12-transformed hamster cell line T637, its revertants, whic h ; have lost most of the >20 Ad12 genome equivalents integrated chrom osomally in cell line T637, and in the Ad12-induced tumor T191. Some o f these junction sites have been molecularly cloned, and the nucleotid e sequences at the sites of transition between viral and cellular DNAs have been determined, The sites of linkage between the hamster cellul ar and the foreign (viral) DNA are characterized by the frequent occur rence of patch homologies between the recombination partners, The cell ular junction sites investigated here are not transcriptionally active , One of the cellular DNA sequences abutting the right Ad12 DNA termin us in cell line T637 (os2) is represented only once in the hamster gen ome and has a strikingly low abundance of 5'-CG-3' dinucleotide sequen ces, One 5'-GCGC-3' sequence close to the Ad12 DNA integration site is heavily methylated in normal cells, Ad12-transformed cells, and Ad12- induced tumor cells, The second such sequence is more remote from the junction site, is partly methylated in BHK21 hamster cells, and shows differences in methylation in different Ad12-transformed cell lines, T his site is unmethylated in liver DNA, The cellular DNA sequence at th e site of Ad12 linkage in the tumor T191 exhibits homologies to highly repetitive sequences of the Alu family and to an origin of hamster DN A replication containing an Alu element, A number of junction sites be tween Ad12 DNA and hamster or mouse DNA in Ad12-transformed cell lines or Ad12-induced tumor cell lines, investigated here and previously, a re characterized by stem-loop structures encompassing the junction sit es.