The Saccharomyces cerevisiae linker histone Hho1p, with two globular domains, can simultaneously bind to two four-way junction DNA molecules.
Saccharomyces cerevisiae encodes a single linker histone, Hho1p, with two globular domains. This raised the possibility that Hho1p could bind to two nucleosome cores simultaneously. To evaluate this idea, we studied the ability of a four-way junction, immobilized on the surface of a magnetic bead, to pull down a radiolabeled four-way junction in the presence of different Hho1 proteins. Four-way junctions are known to bind to H1, presumably due to structure similarities to the DNA at the nucleosomal entry/exit point. We found a significant increase in the ability of full-length Hho1p to pull down radiolabeled four-way junction DNA under ionic conditions where both globular domains could bind. The binding was structure specific, since the use of double-stranded DNA, or a mutant Hho1p in which the second DNA binding site of globular domain 1 was abolished, resulted in a significant decrease in bridged binding. Additionally, bridged binding required a covalent attachment between the two globular domains, since factor Xa protease treatment of the complex formed by a modified Hho1p that contained a factor Xa cleavage site between the two globular domains resulted in a significant release of radiolabeled four-way junction. These findings demonstrated that the two globular domains independently associated with two different four-way junction molecules in a manner that required amino acid residues implicated in structure-specific binding in the nucleosome. We discuss the implication of these findings on the chromatin structure of yeast and propose a model where a single Hho1 protein binds to two serially adjacent nucleosomes.
Schäfer
Georgia
G
Department of Biotechnology, University of the Free State, P.O. Box 339, Bloemfontein, 9300 South Africa.
Smith
Elizabeth M
EM
Patterton
Hugh G
HG
D001483:Base Sequence; D017931:DNA Primers; D006657:Histones / Q000302:isolation & purification / Q000378:metabolism*; D010957:Plasmids; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000302:isolation & purification / Q000378:metabolism*
D017931:DNA Primers; C480035:HHO1 protein, S cerevisiae; D006657:Histones; D029701:Saccharomyces cerevisiae Proteins