Replication of alpha and beta globin DNA sequences occurs during early S phase in murine erythroleukemia cells.

Abstract
Murine erythroleukemia cells (MELC) can be induced to express the characteristics of erythroid differentiation by a variety of agents. Previous studies indicate that an action of inducer, occurring during early S phase, may be critical to the expression of differentiated characteristics such as initiation of accumulation of newly synthesized .alpha. and .beta. globin mRNA. The time of replication of globin genes in MELC was studied. DNA was isolated from synchronous populations of cells obtained by centrifugal elutriation. Newly replicated DNA sequences were prepared from synchronized cells cultured for 1 1/2 h with 5-bromodeoxyuridine; bromodeoxyuridine-containing DNA was isolated by CsCl gradient centrifugation. Cloned probes were used for hybridization to newly synthesized DNA. The .alpha. and .beta. globin gene seq-ences are replicated early in S phase, while ribosomal RNA gene sequences are replicated to about the same extent in early, middle and late S phases.