Histone proteases of avian erythroid cells

Protease activity associated with avian erythroid chromatin has been studied by gel electrophoresis of histones. Histone degradation is minimal at neutral pH, but is readily detected when chromatin is incubated at pH 3, and is evident to a lesser extent at pH 9. As a result of the pH 3 activity, the f1 and f2 chistones are preferentially degraded when the histone complement is DNA-bound, but these histones are relatively resistant to attack when present as free histone. The pH 3 activity reported here has properties similar to those of neutral histone proteases from other tissues, except that it is not inhibited by bisulphite. Added exogenous proteins are not degraded. The activity of avian erythroid histone protease decreases as maturation of the cells proceeds. Since we have previously shown that turnover of DNA-bound f2c histone occurs in reticulocytes and histone synthesis is absent in erythrocytes, it is possible that the histone protease described here may be involved in f2c histone turnover.