SELF-ASSOCIATION OF LINKER HISTONE H5 AND OF ITS GLOBULAR DOMAIN - EVIDENCE FOR SPECIFIC SELF-CONTACTS

The ability of avian-specific linker histone H5, and the globular doma ins of H5 (GH5) and H1 degrees (GH1 degrees), to self-associate either free in solution or when bound to DNA was investigated. All three pro teins underwent a salt-dependent increase in turbidity that may be ind icative of nonspecific interactions. Dithiobis(succinimidyl propionate ) cross-linking was used to measure specific contacts for both H5 and GH5 free in solution and bound to DNA. H5 and GH5 each became cross-li nked in solution, with GH5 displaying divalent polymerization interact ions, which suggests that two specific surfaces were involved in the a ssembly process. For GH5-DNA complexes, cross-linking appeared to be l argely the consequence of aggregation, but under low concentrations of DSP, cross-linking GH5 was observed to assemble preferentially onto D NA before oligomerizing to form massive aggregates. Both linear and su percoiled DNA facilitated GH5 interactions compared to assembly in sol ution; differences in the distribution of cross-linked polymer sizes i ndicates that assembly is dependent on both the presence of DNA and th e morphology of the DNA. Finally, on the basis of a technique referred to as quantitative proteolysis, GH5 assembly on DNA appears to involv e specific protein-protein contacts involving the C terminus of one pa rtner. Overall, the cumulative results reported here support the premi se that linker histones assemble specifically both in solution and on DNA.