INTERACTION OF NUCLEOSOME CORE DNA WITH TRANSITION PROTEIN-1 AND PROTEIN-3 FROM BOAR LATE SPERMATID NUCLEI

The DNA binding properties of boar transition proteins 1 and 3 (TP1 an d TP3) were studied by means of physicochemical techniques, The ultrav iolet difference absorption spectra upon TP1 and TP3 binding to rat li ver nucleosome core DNA (double-stranded DNA) showed TP1- and TP3-indu ced hyperchromicity at 260 nm, 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 1 mM NaC l TP1 and TP3 caused slight stabilization of the DNA against thermal m elting, destabilization of the DNA was observed at 50 mM NaCl. From th e results of quenching of the tyrosine fluorescence of TP1 and the try ptophan fluorescence of TP3 upon their binding to double-stranded and single-stranded boar liver nucleosome core DNA at 50 mM NaCl, the appa rent association constants for the binding of TP1 to double- and singl e-stranded DNA were calculated to be 8.0x10(4) and 1.3X10(5) M(-1), re spectively, and those for the binding of TP3 to double- and single-str anded DNA to be 7.1X10(4) and 1.8X10(5) M(-1), respectively, These res ults suggest that TP1 and TP3, having higher affinity for single-stran ded DNA, induce local destabilization of DNA, probably through the sta cking of Tyr32 and Trp18 with nucleic acid bases, respectively.