Binding of chromosomal non histone proteins to DNA and to nucleohistones. Effect of in vitro phosphorylation

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1. Introduction The possibility that chromosomal non-histone pro- teins (NHP) could be regulators of gene expression in eukaryotic cells is suggested by chromatin reconstitu- tion experiments and by DNA/RNA hybridation ana- lyses [l-2]. These experiments showed that NHP modi- fied transcription in a manner characteristic of the tissue of origin. But the mechanisms by which the NHP was able to interact and to modify the transcription are not completely clear. However, several studies have implied that NHP is able to stimulate the tem- plate activity of nucleohistones, at least partly, through the presence of phosphoproteins and of protein kinases [3]. Similarly, NHP modifications are associated with the stage of the cell cycle and with the differentiation of cells during development and aging [4-81. A direct role for NHP cannot be excluded since some NHP does bind to DNA [9,10] . In chromatin however, large parts of DNA are covered with histones [ 11 ,121. Histones have been demonstrated to play a role in the structure of DNA and in the chromatin conformation [13,14]. They have an inhibitory effect on the transcription availability of DNA. This inhibi- tory action can be partially suppressed by histone- phosphorylation [ 151. In this work we have studied comparatively the binding of NHP to DNA and to formaldehyde-treated nucleohistones, this last technique allowing a cova- lent binding of histones to DNA [12,16]. DNA and formaldehyde-treated nucleohistones (FNH) were f=ed on a cellulose matrix and poured into a column. A small NHP fraction remained bound and could be