A novel repeated element with Z-DNA-forming potential is widely found in evolutionarily diverse eukaryotic genomes

By Southern blotting and hybridization analysis using 32P-labeled poly(dT-dG) . poly(dC-dA) as a probe, we have found, in eukaryotic genomes, a huge number of stretches of dT-dG alternating sequence, a sequence that has been shown to adopt the Z-DNA conformation under some conditions. This sequence was found in all eukaryotic genomes examined from yeast to human, indicating extraordinary evolutionary conservation. The number of the sequence ranged from about 100 in yeast to tens of thousands in higher eukaryotes. Comparison of nucleotide sequences of dT-dG alternating regions and its flanking regions in several cloned genes showed that the repeated element [the Z(T-G) element]] consists only of dT-dG alternating sequence with variable length. The presence of another purine-pyrimidine alternating sequence was also surveyed in eukaryotic genomes by Southern blot hybridization using 32P-labeled poly(dG-dC) . poly(dG-dC) as the probe. The stretches of dC-dG alternating sequence [the Z(C-G) element] were found to be moderately repetitive in human, mouse, and salmon genomes. However, a few and no copies of the Z(C-G) element were found in yeast and calf genomes, respectively. These results provide evidence for the abundance of potential Z-DNA-forming sequences in nature.