Loss of alleles in aprt mutants of CHO cells demonstrated by BclI restriction-fragment-length variation.

A BclI restriction-fragment-length variation (RFLV) has been identified 7 kb downstream of the 3' end of the adenine phosphoribosyltransferase (aprt) gene in the Chinese hamster CHO cell line. This RFLV generates 19 kb and 17 kb + 2 kb BclI fragments. Three other cell lines derived from different Chinese hamsters are homozygous for this RFLV. The 17 kb + 2 kb allele was mapped to the Z4 chromosome based upon the absence of this allele in the CHO-derived hemizygote AA8-5, whose functional allele is known to map to chromosome Z7. The class 2 aprt+/-line D416 loses the 19-kb allele after undergoing the high-frequency (HF) deletion event, indicating that the HF deletion event occurs on the Z7 chromosome. On the other hand, deletion events in the class 3 heterozygote D423 (which do not spontaneously occur at HF) resulted in loss of the 17 kb + 2 kb allele. This is consistent with a previously proposed model holding that the two aprt alleles in the CHO cell line have different inherent probabilities of undergoing a large deletion event.