Abstract

Chick embryo fibroblasts were cultured in vitro up to confluency, after which they were kept in the following different Minimum Essential Media containing a labelled amino acid: ( i) a medium containing 1% calf serum which prevented the cells from dividing; ( ii) a medium containing 30% calf serum which stimulated the cells to divide synchronously; ( iii) a medium without lysine but also containing 1% calf serum which prevented the cells to go beyond G 1. Chromosomal non-histone proteins (NHP) were extracted from cells cultured in these three different media and then were compared individually by gel electrophoresis. The gels were sectioned and the radioactivity measured in each slice. No significant variations were found in the level of radioactivity for individual resting cells ( i) if radioactive lysine (or leucine) was used as a precursor. A peak of radioactivity was observed before the onset of DNA synthesis for cells stimulated to divide ( ii). Whenever lysine was omitted for several hours ( iii) a peak of radioactivity was observed and was shown to be different from the peak found in stimulated cells. The rate of NHP synthesis under these various conditions was studied. Possible biological functions of the non-histone chromosomal protein were discussed.

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