Z-DNA immunoreactivity in rat tissues

Recently, it has been shown that natural and synthetic deoxynucleotide polymers can adopt a left-handed helical structure (termed Z-DNA) in appropriate conditions (see, for example, refs 1 and 2 and the references therein). In contrast to the more familiar right-handed B-DNA, Z-DNA is strongly immunogenic, and polyclonal and monoclonal antibodies against Z-DNA have been elicited. By using such antibodies, immunoreactivity for Z-DNA has been detected in the polytene chromosomes of two dipteran species, in the macronucleus of a ciliated protozoon, and in certain plant nuclei (cited in ref. 11). In view of the possible importance of Z-DNA as a genomic regulatory signal, it would be highly desirable to know whether Z-DNA also occurs in mammals. We have therefore initiated an immunohistochemical study of various rat tissues by using three antisera specific for Z-DNA, and the peroxidase-antiperoxidase technique for visualization of tissue-bound antibodies. Here we demonstrate that the nuclei of many, but not all, types of rat cells exhibit Z-DNA immunoreactivity, suggesting that Z-DNA may exist naturally in mammalian chromatin.