Studies on Chinese hamster ovary mutants showing multiple cross-resistance to oxidative phosphorylation inhibitors

Several stable Chinese hamster ovary (CHO) mutants were selected after ethylmethane sulfonate mutagenesis for resistance to oligomycin, rutamycin, venturicidin, or antimycin. These mutants shared a number of common properties. They exhibited cross-resistance to those drugs which act on oxidative phosphorylation, irrespective of the structure and site of action of the drug. All the mutants showed a reduced ability to grow in suspension and to reach high saturation densities. They were also unable to use galactose as a carbon source. The short lag period required for selection (10–15 days), the similarity of the mutation rates for resistance to each of the four drugs, the high variance/mean ratios in fluctuation tests, and the recessive behavior of the resistance marker in hybrids suggest that the mutations responsible for resistance to oxidative phosphorylation inhibitors in CHO cells are coded by nuclear DNA. Segregation experiments indicated no linkage between the oligomycin-resistant marker (Olg^r) and Thg^r (thioguanine resistance). Oxidative phosphorylation, as measured by the rate of respiration coupled to phosphorylation in whole cells remained as sensitive to the drugs in the mutants as in the parental cell line. Glucose transport and the overall Krebs' cycle activities also appeared similar in the mutants and the wild type. All the mutants had an increased rate of lactic acid production (up to twofold), associated with increased specific activities for several glycolytic enzymes when assayed in cell-free extracts.We wish to dedicate this paper to Dr. Boris Ephrussi one of the founders of the field of somatic cell genetics. Many of the techniques, and more important, the concepts which prevail in this field can be laid to his seminal thinking on the subject. One of us (L.S.) in particular, owes a great deal to his personal stimulation and encouragement over a large number of years.     

Host survival following infection with or induction of bacteriophage lambda mutants

The lethal effects of lambda infection and lambda induction were studied using conditional lethal mutants of phage lambda in the su- host W3350. Phage with mutations in Q and R, which are blocked after DNA replication, kill promptly and efficiently on induction or infection. Infection with mutants defective in O and P, which do not replicate, kills less efficiently, although these mutants do kill effectively at high multiplicity of infection. Heat induction of lysogens carrying DNA defective mutants O or P promptly arrests host DNA synthesis, but this leads to killing only after a considerable lag. Heating also blocks transfer of an F-gal episome by a lysogen in which a temperature inducible O or P mutant is carried on the episome. These effects of heating are reversed by cooling, which leads to recovery of host DNA synthesis and recovery of the ability to transfer the episome. The effects of heating lysogens for temperature inducible DNA defective phage are interpreted to result from interruption of the Escherichia coli chromosome (or episome), which in itself, is not lethal to the host. Their reversal on cooling is attributed to repair of the break in the chromosome, which permits survival, often associated with curing. Evidence is presented that interruption of the E. coli chromosome can also be produced by infection, but the relationship of this event to loss of viability on infection is still uncertain. N mutants kill even less efficiently than O and P mutants on infection and show killing and DNA arrest on thermal induction only after an initial stimulation of DNA synthesis. They neither cure appreciably, nor resume DNA synthesis on cooling, once DNA synthesis is arrested. Not all the properties of N mutants can presently be explained.