ISOLATION AND CHARACTERIZATION OF L-METHIONINE-RESISTANT MUTANTS OF SV40-TRANSFORMED BALB-3T3 (SVT2) AFFECTING L-METHIONINE TRANSPORT

l-Methionine-resistant mutants (metr) of SVT2 have been isolated by a multistep or single-step procedure. They are stable and arise in the absence of the selective agent at a mutation rate of 3.5×10-5. Treatment with EMS raises the frequency of metr mutants 32- to 47-fold. SVT2 transports methionine at an initial rate 4.5 times that of 3T3. The metr mutants have a decreased initial rate of methionine transport. Some mutants had both an increase in Km and decrease in Vm while others had either an increase in Km or decrease in Vm. Kinetic studies permit the identification of two transport systems for methionine for 3T3 and only one for SVT2 and the metr mutants. The Vm for SVT2 is three times larger than for the high-affinity system of 3T3 while the Km's are the same. The change in initial rate of transport of a few specific amino acids besides methionine suggests that affects on transport observed in both transformation and mutation are not due to just a general membrane change. A comparison of the amino acid spectrum of inhibition of independently transformed SV40 cell lines demonstrates that each transformant is unique. © 1979 Plenum Publishing Corporation.