title: DNA looping by Saccharomyces cerevisiae high mobility group proteins NHP6A/B. Consequences for nucleoprotein complex assembly and chromatin condensation.
abstract: The formation of higher order protein.DNA structures often requires bending of DNA strands between specific sites, a process that can be facilitated by the action of nonspecific DNA-binding proteins which serve as assembly factors. A model for this activity is the formation of the invertasome, an intermediate structure created in the Hin-mediated site-specific DNA inversion reaction, which is stimulated by the prokaryotic nucleoid-associated protein HU. Previously, we have shown that the mammalian HMG1/2 proteins substitute for HU in this system and display efficient DNA wrapping activity in vitro. In the present work, we isolate the primary sources of assembly factor activity in Saccharomyces cerevisiae, as measured by the ability to stimulate invertasome formation, and show that these are the previously identified NHP6A/B proteins. NHP6A/B have comparable or greater activity in DNA binding, bending, and supercoiling with respect to HU and HMG1 and appear to form more stable protein.DNA complexes. In addition, expression of NHP6A in mutant Escherichia coli cells lacking HU and Fis restores normal morphological appearance to these cells, specifically in nucleoid condensation and segregation. From these data we predict diverse architectural roles for NHP6A/B in manipulating chromosome structure and promoting the assembly of multicomponent protein.DNA complexes.
authors.affiliation: Molecular Biology Institute, UCLA 90095, USA.
authors.forename: T T
authors.initials: TT
authors.lastname: Paull
authors.forename: R C
authors.initials: RC
authors.lastname: Johnson
mesh_terms: D001483:Base Sequence; D002843:Chromatin / Q000378:metabolism*; D004278:DNA, Superhelical / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D005656:Fungal Proteins / Q000378:metabolism*; D024001:HMGN Proteins; D006609:High Mobility Group Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D002843:Chromatin; D004278:DNA, Superhelical; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D024001:HMGN Proteins; D006609:High Mobility Group Proteins; C086471:NHP6A protein, S cerevisiae; C086472:NHP6B protein, S cerevisiae; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins