A histone heterodimer, designated as p28, which contains an N e (c-glutamyl)lysine cross-link between Gln9 of histone H2B and Lys5 or Lys12 of histone H4, is present in starfish (Asterina pectinifera) sperm. Treatment of spermnuclei with micrococcal nuclease produced soluble chromatin, which was size-fractionated by sucrose-gradient centrifugation to give p28-containing oligonucleosome and p28-free mono-nucleosome fractions, indicating that the cross-link is inter-nucleosomal.
