Complete Amino‐Acid Sequences of DNA‐Binding Proteins HU‐1 and HU‐2 from Escherichia coli

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Abstract
The DNA-binding protein HU from E. coli is a heterodimer constituted of 2 polypeptide chains termed HU-1 and HU-2, of 90 residues each. Their primary structures were established from structural data obtained from tryptic peptides of each monomer in addition to the structural data provided by the automated Edman degradation of the dimer and by peptides derived from cleavage of the dimer with trypsin, chymotrypsin, V8 staphylococcal protease and dilute acid. The amino-terminal and carboxy-terminal sequences of the dimer HU reported previously were confirmed. The amino acid sequences of proteins HU-1 and HU-2 are identical to those of proteins NS-1 and NS-2, respectively, determined independently by Mende et al. The amino acid sequences of proteins HU-1 and HU-2 are closely related but differ by 28 residues. These proteins are characterized by their high content of hydrophobic residues represented mostly by alanine. In both proteins, half of the basic residues are scattered along the polypeptide chain and the remainder is found within 2 short sequences located in the carboxyterminal part of the molecule. No sequence homology could be established between the proteins HU-1 and HU-2 and any 1 of the 5 histones from different eukaryotes.