Possible role of histones in regulation of nucleic acid synthesis

Abstract

ALTHOUGH this paper will be concerned principally with our studies on the possible role of histones in regulation of nucleic acid synthesis, it seems pertinent to comment first upon the gel electrophoresis of histones. Butler has stated that the most satisfactory way of characterizing histones is the application of starch gel electrophoresis [S, 10, 111. We have found [ 121 that polyacrylamide gels are superior to starch gels in the separation of histones, and Reisfeld et al. [ 131 have reported success with this gel system in the electrophoresis of other cationic proteins. The gels are formed by mixing buffered tetramethy-ethylenediamine catalyst with 60 per cent acrylamide and 0.4 per cent N,N’-methylenebisacrylamide followed by addition of ammonium persulfate. The gels are formed in glass tubes and have a pH of 3 after polymerization. Samples are applied directly upon the gels in a density-stabilized layer, and electrophoresis is conducted in a glycine buffer at pH 4 for 4.5 hr at 15 ma. per tube. The gels are stained in amido black, and excess stain is removed electrically. Patterns obtained by electrophoresis of calf thymus histones are shown diagrammatically in Fig. 1 in comparison with patterns obtained by electrophoresis in starch gels. The bands shown in Fig. 1 C were found consistently by electrophoresis in polyacrylamide gels, and the bands are designated by Roman numerals. Bands II and IV, found in all calf thymus histone preparations examined in this laboratory, stained more heavily than the other bands and provided easily recognized and very reproducible reference points. The inclusion of a sample of unfractionated histone in each electrophoretic run of 6 samples facilitated the assignment of band identities in preparations of histone fractions. Band II was arbitrarily assigned a relative mobility (1~‘)