Effects of DNA and urea on the specificity for H1 histone of the neutral protease B partially-purified from rat liver chromatin.

A neutral protease, named protease B in the previous report (Tsurugi, K. & Ogata, K. (1982) J. Biochem. 92, 1369-1381), was partially purified from rat liver chromatin by gel filtration through Sepharose 6B followed by DE-Sephadex column chromatography. The proteolytic activity on total histones of the partially-purified protease B was increased about two fold by addition of DNA and again increased by further addition of 2 M urea. Analysis of the hydrolysed products showed that out of five species of histones, only H1 was degraded in the presence of an amount of DNA equivalent to the amount of histones, whereas core histones were also degraded in the absence or presence of one-tenth amount of DNA. Urea accelerated the selective degradation of H1 histone because H1 histone was preferentially degraded in the presence of even a low amount of DNA. In contrast, core histones became resistant to the protease B in the presence of DNA and/or urea. Heat-denatured DNA stimulated the degradation of H1 histone even in the absence of urea to almost the same extent that native DNA did in the presence of urea. Thus, protease B efficiently degrades H1 histone when its association with DNA is destabilized by either addition of urea or pretreatment of DNA with heat.