Structures of DNA: A Summary

The object of this Cold Spring Harbor Symposium, as Jim Watson put it in his initial invitation, was to discuss the structures of DNA at various levels, ranging from precise crystallogtaphic analysis through the nature of DNA while it is being either replicated or transcribed and then on to the organization, both genetic and physical, of higher chromosomes. The title of the Symposium—"Structures of DNA"—reflects the fact that now, almost 30 years after its discovery, the simple double helix is known to be only one of the conformations or configurations that DNA can adopt. Although the right-handed double helix in the B form remains the basic form, it has been shown that a left-handed helical form, Z-DNA, exists as well. Moreover, the axis of DNA in vivo is normally supercoiled, and in the laboratory it can be made to supercoil in both left- and right-handed senses: In the case of...