Disappearance of Polyribosomes during in vivo Erythroid Maturation and Nuclease Activity

Abstract

DEBELLIS and I have compared the disappearance of ribosomes and polyribosomes during the maturation in vivo of erythroid cells in the rabbit¹. This involved injecting twice labelled cells, obtained from a donor animal, into a recipient animal in which the bone marrow was repressed by continuing injections of colchi-cine. The events which occurred, including disappearance of total erythroid cell RNA, of reticulocytes, and of ribosomes and polyribosomes, were the result of maturation of the donor cells in the recipient circulation, for evidence was presented to show that the donor cells were not removed from the circulation during the time of the study. In contrast to previous work^2–4 there was no disproportionate loss of polyribosomes during erythroid cell maturation. Rowley⁵ criticized these studies because the initial and subsequent sucrose density gradient centrifugation patterns of ribosomes (Fig. 1, upper) resembled those obtained by other workers^6,7 with polyribosomes treated with small amounts of ribonuclease. He concluded that “the similarity in (sucrose density gradient) patterns (as a) function of age simply represents degradation to a uniform state”. No experimental evidence is offered to support this conclusion.