Novel histone H2A-like protein of escherichia coli.

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Abstract
A histone-like protein (H) from E. coli was purified to more than 98% homogeneity by using its capacity to inhibit DNA functions. H protein behaves as a dimer of 28,000-dalton subunits. The histone H2A-like properties of H protein are binding to DNA at a stoichiometry of 1 H protein dimer/75 bases, abundance of about 30,000 molecules/cell, sufficient to bind about 20% of the chromosome, limiting digestion of double-stranded DNA by micrococcal nuclease, reannealing of complementary single-stranded DNA, amino acid composition resembling that of eukaryotic histone H2A, neutralization of H protein by antibody specific for H2A, heat stability, and acid solubility. The capacity of H protein to bind DNA prevents its template or substrate functions in several reactions in vitro: DNA synthesis by several polymerases; transcription by RNA polymerase; DNA topoisomerase activity; and DNA-dependent ATP hydrolysis by rep protein, dnaB protein or protein n''. Together with other histone-like proteins of E. coli, H protein may organize the E. coli chromosome into nucleosomes, such as in eukaryotic chromatin.