ABSTRACT
We have imaged DNA from the calf thymus nucleosome using a scanning tunneling microscope (STM) operated in water. The fragments are deposited onto the interface between a buffer solution and an epitaxially grown gold surface using an electrochemical tecnique. Most of the fragments are fairly straight, and when individual polymers can be identified, their length is consistent with the expected 146 basepairs (approximately 500 A). The resolution is often adequate to show signs of the 36 A helical pitch. Some images show a structure which appears to have abrupt kinks of the sort predicted by Crick and Klug (Nature 255, 530-533, 1975). In order to check that this shape is not a consequence of binding to underlying structure on the gold substrate, we have also made images of kinked structures using an atomic force microscope (AFM) with the DNA bound to glass.
Subject(s)
DNA/ultrastructure , Microscopy, Electron, Scanning , Nucleosomes/ultrastructure , Animals , Cattle , Molecular ConformationABSTRACT
The scanning tunneling microscope can image uncoated DNA submerged in water. The grooves of the double helix were clearly resolved in images of the 146-base pair fragment extracted from calf thymus nucleosome. In contrast to images obtained with dry DNA, the helix pitch varied only a small amount (36 +/- 5 angstroms). The path of the helix shows considerable variation. It is quite straight when the molecules are densely packed, but it curves and bends in isolated molecules.
