GROWTH-RATES OF HPRT AND TK MUTANT CHO CELL-LINES

The growth rates of 31 X-ray-induced hypoxanthine phosphoribosyl trans ferase (hprt) deficient mutants of CHO-KI cells were measured. Mutants had been classified as (1) full-deletion, (2) partial deletion or rea rrangement, or (3) unchanged by Southern blot analyses. No relationshi p between growth rate and deletion type was observed. Even where all h prt-specific bands were missing, proliferation rates in culture were n ormal. Additionally, in CHO-AT3-2 cells, which are heterozygous at the tk locus, no difference in growth rates between a spontaneous hprt mu tant and its parent was observed, although double hprt-tk-/- mutants b rew more slowly.