title: DNA bending by the chromosomal protein HMG1 and its high mobility group box domains. Effect of flanking sequences.
abstract: HMG1 is an evolutionarily highly conserved chromosomal protein consisting of two folded DNA-binding domains, A and B ("high mobility group (HMG) boxes"), and an acidic C-terminal domain. Several lines of evidence suggest that previously reported sequence-independent DNA bending and looping by HMG1 and its HMG box domains might be important for the proposed role of the protein in transcription and recombination. We have used ligase-mediated circularization assays to investigate the contribution of the individual A and B HMG1 box domains and of the linker region between A/B- and B/C-domains, which flank the "minimal" B-domain (residues 92-162), to the ability of the HMG1 protein (residues 1-215) to bend DNA. Neither the minimal B-domain nor the minimal B-domain with a 7-residue N-terminal extension (85TKKKFKD91) bent the DNA. The attachment of an extra 18-residue C-terminal additional extension (residues 163-180) to the minimal B-domain had only a small effect on the ability of the HMG box to bend DNA. On the other hand, circularization assay with a B-domain having both 7-residue N-terminal and 18-residue C-terminal flanking sequences (residues 85-180) revealed a strong bending of the DNA, suggesting that both extensions are a prerequisite for efficient DNA bending by the B-domain. We have also shown that a single lysine residue (Lys90) in a short N-terminal sequence 90KD91 attached to the B-domain is sufficient for strong distortion of DNA by bending, provided that the B-domain is flanked by the 18-residue C-terminal flanking sequence. Although the DNA bending potential of HMG1 seems to be predominantly due to the B-domain flanked by basic sequences, covalent attachment of the A- and B-domains is necessary for efficient DNA flexure and the ability of the (A+B)-bidomain to bend DNA is further modulated in the native HMG1 protein by its acidic C-domain.
authors.affiliation: Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, 612 65 Brno, Czech Republic.
authors.forename: M
authors.initials: M
authors.lastname: Stros
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D006609:High Mobility Group Proteins / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D051381:Rats
chemical_list: D006609:High Mobility Group Proteins; D004247:DNA