Existence of differences in repressor properties between serine-rich histones (H5, F2c) from immature and mature pigeon erythroid cells.

The abilities of H1 and H5 histones from immature and mature pigeon erythroid cells and subfractions of H5 histones with different content of alkali-labile phosphorus to restrict RNA synthesis were compared in an in vitro transcription system with bacterial RNA polymerase. It has been found that: a) H1 histones from both sources exhibit similar efficiency. b) H5 histones from immature cells restrict transcription to a lesser extent than the same histone from the mature erythrocyte. c) The subfraction of H5 histone from immature cells with the higher content of alkali-labile phosphorus restrict transcription less than the subfraction with the lower degree of phosphorylation. The results suggest that H5 histone, which first appears in the erythroblasts in a highly phosphorylated form, does not display its potential 'repressor' properties. During erythrocyte maturation H5 histone is dephosphorylated and this causes the massive inactivation of erythrocyte genome.