title: Oligomerization of Hmo1 mediated by box A is essential for DNA binding in vitro and in vivo.
abstract: Hmo1, a member of HMGB family proteins in Saccharomyces cerevisiae, binds to and regulates the transcription of genes encoding ribosomal RNA and ribosomal proteins. The functional motifs of Hmo1 include two HMG-like motifs, box A and box B, and a C-terminal tail. To elucidate the molecular roles of the HMG-like boxes in DNA binding in vivo, we analyzed the DNA-binding activity of various Hmo1 mutants using ChIP or reporter assays that enabled us to conveniently detect Hmo1 binding to the promoter of RPS5, a major target gene of Hmo1. Our mutational analyses showed that box B is a bona fide DNA-binding motif and that it also plays other important roles in cell growth. However, box A, especially its first α-helix, contributes to DNA binding of Hmo1 by inducing self-assembly of Hmo1. Intriguingly, box A mediated formation of oligomers of more than two proteins on DNA in vivo. Furthermore, duplication of the box B partially alleviates the requirement for box A. These findings suggest that the principal role of box A is to assemble multiple box B in the appropriate orientation, thereby stabilizing the binding of Hmo1 to DNA and nucleating specific chromosomal architecture on its target genes.
authors.affiliation: Isotope Center, Tokyo University of Agriculture, Setagaya, Tokyo, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Kasahara
authors.affiliation: Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan.
authors.forename: Ayako
authors.initials: A
authors.lastname: Higashino
authors.affiliation: Department of Frontier Bioscience, Hosei University, Koganei, Tokyo, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Unzai
authors.affiliation: Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Yoshikawa
authors.affiliation: Graduate School of Medical Life Science, Yokohama City University, Yokohama, Kanagawa, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Kokubo
mesh_terms: D004271:DNA, Fungal / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D024742:HMG-Box Domains / Q000235:genetics; D006609:High Mobility Group Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D011485:Protein Binding; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D004271:DNA, Fungal; D004268:DNA-Binding Proteins; C103154:HMO1 protein, S cerevisiae; D006609:High Mobility Group Proteins; D029701:Saccharomyces cerevisiae Proteins