Molecular characterization of multilocus deletions at a diploid locus in CHO cells: association with an intracisternal-A particle gene.

The nature of multilocus deletions eliminating the adenine phosphoribosyltransferase (aprt) gene was analyzed in a CHO cell strain heterozygous for this locus. These deletions arose at a high frequency, spanning an estimated average length of 4250 kb. To detect breakpoints participating in their formation, a 200-kb region surrounding aprt was screened for novel fragments. Seven novel fragments were detected, five of which were clustered around the aprt gene itself. Despite the existence of at least eight Alu-equivalent repeats in this region, no breakpoints fell within these elements. Two deletions were characterized in more detail by cloning and sequencing their junction fragments. The novel DNA detected at one junction was unique, whereas that situated at the junction of the other deletion was of a repetitive nature, consisting of a truncated intracisternal-A particle gene. The contrasting nature of these junctions may imply that multilocus deletions of aprt can occur by one of several mechanisms.