BINDING OF HISTONES H1 AND H5 AND THEIR GLOBULAR DOMAINS TO 4-WAY JUNCTION DNA

We have compared chicken erythrocyte linker histones H1 and H5 binding to a synthetic four-way DNA junction. Each histone binds to form a si ngle complex, with an affinity which permits competition against a lar ge excess of linear duplex DNA. The affinity of H5 is higher than that of H1. The globular domain from either protein will also bind strongl y, but in this case multiple binding occurs. Binding of intact H1 is i nhibited by cations: Mg2+ and spermidine are very effective, Na+ much less so. This inhibition is not likely to be a general ion-competition effect, for Mg2+ is much less effective in inhibiting the binding of H1 to linear DNA. Instead, the inhibition of binding;may be due to ion -dependent changes in the conformation of the four-way junction, which are known to occur under similar conditions. These results strongly s uggest that the angle formed between the arms of the DNA junction coul d be a major determinant in the interaction of H1 with DNA crossovers.