THE C-DOMAIN IN THE H1 HISTONE IS STRUCTURALLY CONSERVED

The C-domain of H1 is conserved in composition and not in sequence. The following regularities have been identified: the distribution of lysine, alanine and proline is non-random; alanine occurs in doublets and at intervals of 4-6 significantly more often than expected for random sequences of equal composition; and lysine also deviates from random distribution in that doublets are under-represented and intervals of 2-7 are over-represented. Lysine preferentially occurs in singlets and alanine in doublets rather than triplets or quadruplets. This discourages the formation of helices without neutralization of lysine charges. When lysine residues are paired with DNA phosphate residues, helices are highly probable. Interproline spacing promotes short helical segments. The regularities arising from the conservation of composition and non-random residue distribution suggests that C-domains adopt similar structures and in fact are structurally conserved.