Rapid exchange of histones H2A and H2B in sea urchin embryo chromatin

Chromatin from sea urchin blastula and gastrula was partially digested with micrococcal nuclease and separated electrophoretically in two dimensions into various nucleosome fractions and their component histones. After labelling of the embryos with radioactive lysine the various isohistones of the H2A and H2B group in all nucleosome fractions had incorporated approximately twice as much the radioactivity as the histones H2 and H4. The results are interpreted in terms of a labile nucleosome structure during transcription.