Characterization of a novel, low-molecular-weight DNA-binding protein from Escherichia coli.

Abstract

A low-molecular-weight (7000), heat-stable protein-HU-that stimulates transcription of bacteriophage X DNA by E. coli RNA polymerase was purified from E. coli extracts using affinity chromatography on DNA-cellulose. HU binds to native DNA, resulting in an apparent thickening of the DNA chains as revealed by electron microscopy. Contrary to DNA unwinding proteins, it causes no destabilization of the double helix. HU differs from previously described transcription factors (HI, D, etc.) and from the lowmolecular-weight w subunit of the RNA polymerase. By its amino-acid composition and characteristics, HU displays an interesting. resemblance to some eukaryotic histones, such as H2B and Hi. A variety of low-molecular-weight proteins from Escherichia coli that stimulate RNA synthesis in vitro have been characterized (1-8). The heat-stable protein, HI (1, 2), was shown to enhance X-lac DNA transcription by E. colt RNA polymerase (3) while causing reduction of ribosomal RNA synthesis in an E. coli DNA-dependent system (4). A heatstable protein, the D factor, was reported to increase the specificity of X-DNA transcription by the E. colt polymerase (5). Another class of small, heat-stable proteins has also been described which stimulates in vitro the replication of RNA bacteriophage (6, 7). That these small protein factors could act by locally affecting the stability of nucleic acid secondary structure, hence favoring or inhibiting the action of polymerases, has already been suggested (1, 2, 5, 8), and it has been proposed that some of these entities, such as the H1 and the D factors, could represent the prokaryotic counterpart of eukaryotic nuclear proteins (3,(5)(6)(7)(8).In. the frame of this hypothesis, we have undertaken a more systematic analysis of DNA binding proteins by means of affinity chromatography on DNA-cellulose columns. We report, here, the purification from E. coli extracts of a small, heat-stable protein-HU-that stimulates transcription of bacteriophage X-DNA and displays by its amino-acid composition and physicochemical behavior some properties characteristic of eukaryotic histones. Fig. 1 MATERIALS AND METHODS Bacterial

New insights into plastid nucleoid structure and functionality

“…They hence belong to those DNA-binding proteins biochemically detected in thylakoids and nucleoid fractions (Briat et al 1984;Bülow et al 1987;Nemoto et al 1988;Yurina et al 1988;Baumgartner and Mullet 1991) that could have functionally replaced the bacterial histone-like HU (for histone-like protein from E. coli strain U93) proteins which are involved in formation of nucleosome-like structures in bacterial chromosomes (Rouviere-Yaniv and Gross 1975). Among these proteins are several low molecular weight proteins (10-20 kDa) detected by cross-reaction with antibodies directed toward the bacterial HU (Briat et al 1984).…”

The Bacterial Histone-like Protein HU Specifically Recognizes Similar Structures in All Nucleic Acids

“…The Escherichia coli HU protein is a major component of the bacterial nucleoid (1)(2)(3). This small basic histone-like protein that can introduce negative supercoiling into a close circular DNA molecule in the presence of topoisomerase I is highly conserved and found in all bacterial species (4 -7).…”

“…HU belongs to the family of architectural nuclear proteins that control DNA topology by introducing bends into doublestranded (ds) 1 DNA and stabilize higher-order nucleoprotein complexes. HU resembles eukaryotic proteins of the high mobility group (HMG) class in its DNA binding properties because it binds dsDNA with low affinity and no sequence specificity.…”

Regulation of polyamine biosynthesis in Escherichia coli by basic proteins.

“…Several basic histone-like proteins have been isolated from E. coli (24)(25)(26)(27). Proteins H (27) and HU (24) are among those whose amino acid compositions are known.…”