Structural and functional hemi- and dizygous Chinese hamster chromosome 2 gene loci in CHO cells

Fourteen independent somatic cell hybrid clones made between diphtheria toxin (DT)-resistant mouse Cl1D cells and DT-sensitive Chinese hamster ovary (CHO) cells slowly segregated CHO chromosome. Concordant segregation analysis of electrophoretically resolvable Chinese hamster chromosome 2 gene products and CHO chromosomes 2 and Z2 (having q1-q24 deletion) in DT-selected and control hybrid subclones was conducted. Analysis revealed that loci for DT sensitivity and galactose-1-phosphate uridyltransferase could be regionally assigned to Chinese hamster chromosome 2q1-24 and were physically hemizygous in CHO cells. Enolase (ENO1), 6 phosphogluconate dehydrogenase (PGD), and phosphoglucomutase 1 (PGM1) were located outside the q1-24 region on Chinese hamster chromosome 2 and were dizygous in CHO cells. Functional dizygosity of ENO1, PGD, and PGM1 in CHO cells, as determined by the isolation of diploid heterozygous electrophoretic shift mutants following UV and EMS exposure, confirmed their location outside the Z2 deletion and indicated that the deletion did not result in the inactivation of adjacent loci. These results are discussed in relation to current theories on the basis for high frequency of drug-resistant autosomal recessive mutants in CHO cells and conservation of mammalian autosomal linkage groups.