Interaction of Nucleosome Core DNA with Transition Proteins 1 and 3 from Boar Late Spermatid Nuclei

Abstract

The DNA binding properties of boar transition proteins 1 and 3 (TP1 and TP3) were studied by means of physicochemical techniques. The ultraviolet difference absorption spectra upon TP1 and TP3 binding to rat liver nucleosome core DNA (double-stranded DNA) showed TP1- and TP3-induced hyperchromicity at 260nm, which is suggestive of local melting of DNA. CD measurements of TP1-DNA and TP3-DNA complexes indicated that the binding of TP1 and TP3 induced different conformational changes in DNA, probably including local melting of DNA. Thermal melting studies on the binding of TP1 and TP3 to DNA showed that although at 1mM NaCl TP1 and TP3 caused slight stabilization of the DNA against thermal melting, destabilization of the DNA was observed at 50mM NaCl. From the results of quenching of the tyrosine fluorescence of TP1 and the tryptophan fluorescence of TP3 upon their binding to double-stranded and single-stranded boar liver nucleosome core DNA at 50mM NaCl, the apparent association constants for the binding of TP1 to double- and single-stranded DNA were calculated to be 8.0×10⁴ and 1.3×10⁵M^-1, respectively, and those for the binding of TP3 to double- and single-stranded DNA to be 7.1×10⁴ and 1.8×10⁵M^-1, respectively. These results suggest that TP1 and TP3, having higher affinity for single-stranded DNA, induce local destabilization of DNA, probably through the stacking of Tyr32 and Trp18 with nucleic acid bases, respectively.