Sequence determinants for H1 binding on Escherichia coli lac and gal promoters.

The H1 protein is a likely candidate for structuring DNA in the bacterial nucleoid. We have studied determinants leading to its binding to DNA (and in particular to Escherichia coli lac and gal promoters) in vitro through the pattern of attack of both DNaseI and the copper-o-phenanthroline complex [(OP)2Cu+]. The binding of H1 depends on the primary sequence of DNA. H1 also associates with recognition sites for specific proteins, in particular with the Pribnow box and the CRP binding site. Binding of H1 to the Pribnow box of the wild-type lac promoter does not change the pattern of nucleolytic digestion with (OP)2Cu+. In contrast, binding of H1 to the strong lac promoter mutants Ps and UV5 appears to change the conformational state of this DNA. Similar changes in accessibility of the minor groove surrounding the respective binding sites were observed for both H1-DNA and CRP-DNA complexes.