Abstract
The size of the deoxyribonucleoside triphosphate pools of vitamin B-12-deficient cells of E. gracilis, and of vitamin B-12-deficient cells repleted with the vitamin, were measured. The pools were very small, if they exist at all, in deficient cells but expanded rapidly with the addition of the vitamin. The sizes of the pools decreased when DNA synthesis was completed, and were very small when the cells began to divide.