Complete sequence of Sipunculus nudus erythrocyte histone H2B and its gene. Identification of an N,N-dimethylproline residue at the amino-terminus.

The complete amino acid sequence (122 residues) of histone H2B from erythrocytes of the marine worm Sipunculus nudus, has been established from sequence analysis of peptides generated by highly specific cleavage of the protein and from the nucleotide sequence of the encoding gene. The isolation of the H2B gene was facilitated by using a highly specific nucleotide probe, devised from amino acids 58-68 of the protein. The presence of an N,N-dimethylproline residue at the amino-terminus of the protein was established from data provided by mass spectrometry and NMR spectroscopy. This unusual post-translational modification of histone H2B generates a stable positive charge which could strongly interact with the linker DNA.