Spleen Cell Phosphorylation of Salt Soluble Nuclear Protein from Isoproterenol Treated and Sorted Nuclei

Publisher Website
Google Scholar
Abstract
The effect of isoproterenol (IPR) on phosphorylation of acidic nuclear proteins was investigated by two-dimensional gel autoradiography. Mouse spleen cells stimulated to divide by the mitogen concanavalin A (Con A) were separated according to cell cycle stage by flow microfluorometric technique. Exposure of cells for 48 h to 4 μg IPR/ml culture medium produced no significant change in the proportion of S and G 2 phase cells, while a cumulative dose of 8 μg IPR/ml caused a significant repression in DNA synthesis and a reduction in the number of nuclei in G 2 + M phase. Four μg IPR/ml stimulated the greatest amount of G 0 +G 1 phosphorylation of nuclear protein. Several proteins from G 0 +G 1 and S nuclei incorporated 32 P after Con A+IPR administration, and one protein from S phase nuclei revealed intensified labeling at the 8 μg cumulative IPR dose but not at the 4 μg dose. The isolated proteins (W, X, Y, and Z) were reassociated with homologous DNA, centrifuged in a sucrose gradient and shown to co-sediment with DNA. S phase nuclear protein X-S, which was found to be a mixture of proteins (X 0 and X 1 ), was the only exception. One component of X-S, X 0 bound to DNA, while component X 1 failed to bind. Chymotryptic and V 8 protease digests of all isolated proteins were made and analyzed by autoradiography. Proteins X 0 and X 1 , recovered from the sucrose gradient, possessed dissimilar fragment patterns. It is concluded that protein X-S is composed of two proteins (X 0 and X 1 ), one of which (X 1 ) appears during S phase during the 8 μg IPR induced nuclear repression.

This publication has 2 references indexed in Scilit: