Exposed hydrophobic regions in histone oligomers studied by fluorescence

Abstract

The interaction of the fluorescent hydrophobic probe 1-anilinonaphthalene-8-sulfonate (ANS) with histone oligomers and with histone H1 has been studied. The enhancement of ANS fluorescence produced by histones Hν (a roughly equimolar mixture of histones H2A, H2B, H3 and H4) in 2.0 M NaCl, pH 7.5, is higher than that produced by histone H1 under identical conditions. In addition, the fact that the wavelength of maximum emission of the H1-ANS complex is larger than that of the Hν-ANS complex indicates that histone H1 has a weaker hydrophobic character than histones Hν. The increase in ANS concentration produces a red shift of the emission maximum of the Hν-ANS complex, indicating some heterogeneity in the ANS binding sites. Both the H2A-H2B and the H3-H4 complexes cause a similar enhancement of the ANS fluorescence. Trypsin digestion of N-terminal sequences of histones Hν produces only small changes in the intensity of ANS fluorescence. This result produces only small changes in the intensity of ANS fluorescence. This result indicates that the hydrophobic regions of histones Hν to which ANS binds are not located in the N-terminal portions of histone sequences. It is suggested that these exposed hydrophobic regions may be important in the maintenance of chromatin structure.