The Complete Amino‐Acid Sequence of Histone H2B(2) from Sperm of the Sea Urchin Parechinus angulosus

Sperm histone H2B(2)Parechinus consists of a single polypeptide chain of the following 143 amino acids: Pro‐Arg‐Ser‐Pro‐Ala‐Lys‐Thr‐Ser‐Pro‐Arg‐Lys‐Gly‐Ser‐Pro‐Arg‐Lys‐Gly‐Ser‐Pro‐Ser‐Arg‐Lys‐Ala‐Ser‐Pro‐Lys‐Arg‐Gly‐Gly‐Lys‐Gly‐Ala‐Lys‐Arg‐Ala‐Gly‐Lys‐Gly‐Gly‐Arg‐Arg‐Arg‐Arg‐Val‐Val‐Lys‐Arg‐Arg‐Arg‐Arg‐Arg‐Arg‐Glu‐Ser‐Tyr‐Gly‐Ile‐Tyr‐Ile‐Tyr‐Lys‐Val‐Leu‐Lys‐Gln‐Val‐His‐Pro‐Asp‐Thr‐Gly‐Ile‐Ser‐Ser‐Arg‐Ala‐Met‐Ser‐Val‐Met‐Asn‐Ser‐Phe‐Val‐Asn‐Asp‐Val‐Phe‐Glu‐Arg‐Ile‐Ala‐Gly‐Glu‐Ala‐Ser‐Arg‐Leu‐Thr‐Ser‐Ala‐Asn‐Arg‐Arg‐Ser‐Thr‐Val‐Ser‐Ser‐Arg‐Glu‐Ile‐Gln‐Thr‐Ala‐Val‐Arg‐Leu‐Leu‐Leu‐Pro‐Gly‐Glu‐Leu‐Ala‐Lys‐His‐Ala‐Val‐Ser‐Glu‐Gly‐Thr‐Lys‐Ala‐Val‐Thr‐Lys‐Tyr‐Thr‐Thr‐Ser‐Arg. In a previously published partial sequence positions 25, 34, 40 and 41 were incorrectly assigned. The amino‐terminal one third of sperm histone H2B(2)Parechinus is highly basic containing a repeating pentapeptide occurring over the first 24 residues. This repeating pentapeptide is different to that of sperm histone H2B(1)Parechinus. In this region there is very little amino acid sequence homology between H2B(1)Parechinus, H2B(2)Parechinus on the one side and H2Bcalf thymus on the other side, but all three proteins are highly basic in their N‐terminal parts. The carboxyl‐terminal two thirds of sperm histone H2B(2) is hydrophobic except for a short polar region of 20 amino acids. The carboxyl‐terminal region shows a very high amino acid sequence homology between the three H2B histones. Much of the variability occurs in the short polar region whereas the hydrophobic regions are almost completely constant. The majority of the amino acid substitutions that occur in the carboxyl end are conservative. The three H2B protein sequences are compared and the functional and evolutionary significance of the changes is discussed.