THE N TAILS OF HISTONES H3 AND H4 ADOPT A HIGHLY STRUCTURED CONFORMATION IN THE NUCLEOSOME

The histone N tails correspond to conserved amino acid sequences that are peripherally located in the nucleosome and undergo a variety of po st-synthetic modifications during cell cycle. These N tails have been recently recognized as directly interacting with transcription-related proteins. We show here, based on circular dichroic evidence, that the N tails of both tetrameric histones H3 and H4 are highly organized as DNA-bound polypeptide segments in the nucleosome core particle, with about half of their residues, taken together, being alpha-helical. Ln contrast, the N tails of both dimeric histones H2A and H2B are found e ssentially in a random-coil conformation. The implications of these fi ndings on nucleosome structure and recognition are discussed. (C) 1997 Academic Press Limited.