Growth rates of hprt and tk mutant CHO cell lines

The growth rates of 31 X-ray-induced hypoxanthine phosphoribosyl transferase (hprt) deficient mutants of CHO-K1 cells were measured. Mutants had been classified as (1) full-deletion, (2) partial deletion or rearrangement, or (3) unchanged by Southern blot analyses. No relationship between growth rate and deletion type was observed. Even where all hprt-specific bands were missing, proliferation rates in culture were normal. Additionally, in CHO-AT3-2 cells, which are heterozygous at the tk locus, no difference in growth rates between a spontaneous hprt mutant and its parent was observed, although double hprt-tk-/- mutants grew more slowly.