Z — DNA and chromosome structure

Antibodies recognizing the left-handed Z-conformation of DNA bind to polytene chromosomes of D. melanosaster in a specific pattern. The sequences recognized, many in interbands and some in bands, must be either in the Z-form in vivo or preferentially susceptible to conversion to Z-form by cytological procedures. Monoclonal antibody studies strongly suggest that these Z-form sequences are predominantly (dC-dA)n.(dG-dT)n. In situ hybridization experiments show what appear to be long stretches of (dC-dA)n.(dG-dT)n in sites that do not bind antibody. Thus it seems that the formation of Z-DNA in the polytene chromosomes is determined not only by the DNA nucleotide sequence but also by other aspects of chromatin structure in the region of the conformational change.