HYBRIDIZATION OF HAMSTER CELLS WITH HIGH AND LOW FOLATE REDUCTASE ACTIVITY*

  1. John W. Littlefield
  1. GENETICS UNIT, CHILDREN'S SERVICE, BOSTON
  2. HUNTINGTON MEMORIAL LABORATORIES, MASSACHUSETTS GENERAL HOSPITAL, BOSTON
  3. DEPARTMENT OF PEDIATRICS, HARVARD MEDICAL SCHOOL, BOSTON

Abstract

These studies concern the question whether diffusible repressors control the syntheses of enzymes in mammalian cells. First, clonal sublines of baby hamster kidney (BHK 21/13) cells in culture were selected in stepwise fashion for resistance to aminopterin. These sublines survived in concentrations of aminopterin that were up to 104 times higher than those tolerated by wild-type cells because they contained up to 125 times as much folate reductase, probably due to overproduction of the enzyme. When five resistant sublines were hybridized to wild-type lines, 32 of 35 hybrid clones contained intermediate levels of reductase activity. This suggests that overproduction of reductase is not due to loss of a diffusible repressor.

Footnotes

  • ↵ * This work was supported by USPHS grant CA-04670.

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  1. PNAS 1969-01 vol. 62 no. 1 88-95
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