Fine control of DNA synthesis in developing chick red blood cells

Abstract

During complete inhibition of protein synthesis, a homogeneous population of immature chick red blood cells continues to synthesize DNA but at half the control rate. Synthesis in this situation is linear and continues for approximately 50 minutes before exponential inhibition begins. Inhibition of DNA synthesis occurs within 25 seconds after the inhibition of protein synthesis. Absence of protein synthesis does not affect DNA synthesis at the levels of (a) membrane permeability and uptake of label, (b) nucleotide metabolism, (c) a specific subpopulation of cells or (d) a specific sub-population of replicons. In addition, it is shown that protein synthesis is not required for the elimination of an inhibitor of DNA synthesis. No qualitative differences could be found between DNA synthesized in the absence of protein synthesis and DNA made in control cells. Quantitative differences were, however, observed in the rate of DNA chain elongation (70 base pairs per second in control cells compared with 35 base pairs per second in cycloheximide-treated cells). The results are discussed in terms of (a) the function of such a tight coupling, (b) the time constants involved in the synthesis and removal of the coupling protein and (c) the characteristics of this protein which can be used for its identification.