SCANNING TUNNELING MICROSCOPY OF A LIQUID-CRYSTALLINE PHASE OF POLY((DA-DT).(DA-DT)) INDUCED BY A HISTONE H-1 PEPTIDE

In this report, we present the first observations of uncoated poly((dA-dT).(dA-dT)) molecules organized in a liquid crystalline phase induced by the binding of a histone H-1 peptide. The effect of the peptide on the polymer condensation is clearly illustrated on the large-scale STM images which reveal a well defined spacing between parallel DNA helices. High resolution images of rare isolated molecules of poly((dA-dT).(dA-dT)) exhibit two sets of helical pitch values, 6 and 7.5 nm. While the lower value can be correlated with the pitch of poly((dA-dT).(dA-dT)), the larger one may arise from peptide binding in the polymer minor groove.