The metabolism of basic proteins in HeLa cell nuclei.

Abstract

Three basic protein bands (histones) were isolated from HeLa cell nuclei by extraction with 0.02 [image] H2SO4 and electrophoretic separation on polyacrylamide gel. The metabolism of these proteins was studied during different phases of the cell cycle, using cultures synchronized by treatment with amethopterin or high levels of thymidine. In the absence of DNA synthesis the amount of basic nuclear protein did not change, but isotopic studies showed that a certain fraction underwent turnover. During the period of synchronous DNA synthesis, incorporation into the protein bands increased greatly, and the amount of basic proteins doubled. At that time a form which had been synthesized previously, but was not extracted with the banded nuclear proteins during interphase, contributed to the extractable basic nuclear proteins. The 3 electrophoretically isolated proteins displayed generally similar metabolic patterns, but differences were observed which imply that they behave independently.