Covalent linkage of adjacent Thymine-Thymine
(T^T) pairs
Pyrimidine dimers
(typically between adjacent T^T bases) form when
DNA is exposed to Ultraviolet light.
The covalent linkage of
adjacent T residues as a four-carbon cyclo-butyl
ring is reversible by photoreactivation.
Figure ©2012 TA Brown, Introduction
to Genetics (1st ed.); additional
text ©2014 by Steven M. Carr