DNA chain elongation rates in marrow cells from vitamin B12‐deficient patients and methotrexate‐treated mice

Abstract
The DNA synthesized by marrow cells from patients with vitamin B12 deficiency (megaloblastic anemia patients) and mice previously given methotrexate (MTX) was investigated. Suspensions of bone marrow cells were pulse-labeled with [methyl-3H]thymidine or deoxy [5-3H]cytidine for 30 s and the radioactivity in the DNA was chased thereafter in the presence of 10 .mu.M nonradioactive nucleoside for periods up to 60 min. The rates of elongation of new daughter strands were then assessed by hydroxyapatite chromatography of alkali-denatured DNA samples. No significant differences were found between the average rates of elongation of daughter strands from control marrow cells and these from vitamin B12-deficient or methotrexate-affected cells. This is in contrast with results of previous studies which showed a retardation in the rates of movement of replication forks in stimulated, cultured lymphocytes obtained from vitamin B12- or folate-deficient patients.

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