SELECTION OF A LYSINE-RESISTANT CHO-K1 MUTANT WITH REDUCED AMINO-ACID-TRANSPORT THROUGH MULTIPLE SYSTEMS

High levels of L-lysine were used to select for resistant variants of Chinese hamster ovary (CHO-K1) cells. Surviving colonies were screened for altered lysine transport and two with reduced uptake were picked Clone CH-K(r), derived from the more severely affected colony, was ana lyzed in detail. In starved cells the V(max) of lysine uptake in CH-K( r) was half that of CHO while K(m) was unaltered The intracellular poo l of lysine, a substrate of cationic amino acid transport system y+, w as significantly lower in CH-K(r). However, transport and pools of oth er amino acids, which are not substrates of y+, were also reduced in C H-K(r), as was the internal sodium concentration, while hexose import was increased. It appears that the mutation in CH-K(r) is pleiotropic, affecting some general aspects of amino acid transport.