Non-histone chromosomal proteins from virus-transformed and untransformed 3T3 mouse fibroblasts.

A peak in the non-histone chromosomal protein polyacrylamide gel electrophoresis profiles has been detected which is higher in log phase 3T3 and 3T3/SV40 cells than in density-inhibited 3T3 cells. Radioactive incorporation is substantially higher into this peak in log phase 3T3 than in 3T3/SV40 and density-inhibited 3T3 cells. Reversion of 3T3/SV40 cells with dibutyryl cyclic AMP and theophylline produces increased radioactive incorporation into the peak. Electrophoresis of non-histone chromosomal proteins extracted at different stages of the cell cycle in density inhibited 3T3 cells following serum stimulation shows a cyclic variation in the amount of this peak with maximum accumulation in late G1. In contrast the height of an equivalent peak in synchronously growing 3T3/SV40 cells remains constant throughout the cell cycle. It is postulated that the protein(s) of this peak may have a regulatory role in cell growth.