Non-histone chromatin proteins of B lymphocytes stimulated by lipopolysaccharide. III. De novo synthesis.

Nuclear and cytoplasmic proteins synthesised by mouse lymphocytes stimulated in vitro by the B lymphocyte mitogen, lipopolysaccharide, have been analysed by one- and two-dimensional polyacrylamide gel electrophoresis at early and later times after the onset of stimulation. During the first 4 h no change was observed in the electrophoretic profiles but differences in turnover of various nuclear proteins within the same sample were noted. This is contrasted with the previous observations that phosphorylation of nuclear proteins is stimulated within 2 h. (Stott, D.I. and Williamson, A.R. (1978) Biochim. Biophys. Acta 521, 739-752). During prolonged culture, synthesis of nucleoplasmic proteins declined between day 2 and day 3, being reduced to undetectable levels at the end of the 3-day culture period. In contrast, synthesis of many non-histone chromatin proteins was stimulated between 24 and 48 h, the time course and degree of stimulation varying between different proteins. Certain proteins appeared to be synthesized de novo. These events occur at a time of rapidly increasing IgM synthesis and cell differentiation. It is suggested that an initial step in B lymphocyte triggering may involve phosphorylation of preexisting nuclear proteins leading to gene activation followed by synthesis and phosphorylation of new gene regulatory molecules.