Phage Ø29 Protein p6 Is in a Monomer-Dimer Equilibrium That Shifts to Higher Association States at the Millimolar Concentrations Found in Vivo

详细信息    查看全文

• 作者：A. M. Abril ; M. Salas ; J. M. Andreu ; J. M. Hermoso ; and G. Rivas
• 刊名：Biochemistry
• 出版年：1997
• 出版时间：September 30, 1997
• 年：1997
• 卷：36
• 期：39
• 页码：11901 - 11908
• 全文大小：217K
• 年卷期：v.36,no.39(September 30, 1997)
• ISSN：1520-4995

文摘

Protein p6 from Bacillus subtilis phage Ø29(M_r = 11 800) binds in vitro toDNA forming alarge nucleoprotein complex in which the DNA wraps a multimeric proteincore. The high intracellularabundance of protein p6 together with its ability to bind the wholeØ29 DNA in vitro strongly suggeststhat it plays a role in viral genome organization. We havedetermined by sedimentation equilibriumanalysis that protein p6 (1-100 M range), in the absence of DNA,is in a monomer-dimer equilibrium,with an association constant (K₂) of ~2 ×10⁵ M^-1. The intracellularconcentration of protein p6 (~1mM) was estimated measuring the number of copies per cell (7 ×10⁵) and the cell volume (1 ×10^-15L). At concentrations around 1 mM, protein p6 associates intooligomers. This self-association behavioris compatible with a dimer-hexamer model (K_2,6= 3.2 × 10⁸ M^-2) or with anisodesmic association ofthe dimer (K = 950 M^-1), becausethe apparent weight-average molecular mass(M_w,a) does not reachsaturation at the highest protein concentrations. Thesedimentation coefficients of protein p6 monomerand dimer were 1.4 and 2.0, respectively, compatible with translationalfrictional ratios (f/f_o) of 1.15and1.30, which slightly deviate from the hydrodynamics of a rigid globularprotein. Taking together theseresults and considering the structure of the nucleoprotein complex, wespeculate that the observed oligomersof protein p6 could mimic a scaffold on which DNA folds to form thenucleoprotein complex in vivo.