DNA Synthetic rate and DNA content of nucleated erythroid cells

Abstract

Measurements of relative DNA content and DNA synthetic activity have been made on individual cells by autoradiographic measurement of 14C-thymidine incorporation and microphotometric estimation of Feulgen reactivity on the same cells. It has been shown that mean DNA synthetic rate, as measured by label incorporation, does not vary during the synthetic phase; however, at the beginning and end of the S period average synthetic rate is reduced. The variability in individual grain counts is not reduced by classification of the cells according to location in the S period. It has also been shown that G1 does not appear to exist for dog bone marrow normoblasts and that some cells appear to synthesize DNA without incorporation of the labeled precursor. There is evidence provided that DNA synthesis may be to a certain extent an intermittent process depending upon the chromosome replication patterns in individual nuclei. A model of nuclear DNA replication is presented which is consistent with the observed facts.