Inhibition of eukaryotic tRNA transcription by potential Z-DNA sequences.

Abstract
The effect of d(CA/TG)n DNA segments on tRNA transcription has been examined. Alternating purine‐pyrimidine tracts were cloned at a long distance from, adjacent to, or within the coding sequence of a tRNAPro gene from Caenorhabditis elegans and shown to be able to assume the A‐DNA conformation in vitro in physiological salt concentrations. The transcriptional level of these constructs was compared to that of normal tDNAPro by micro‐injection into Xenopus laevis oocytes. Our results show a strong inhibitory effect by potential Z‐DNA sequences only when these are placed in the flanking regions of the gene or when they are located between the elements (Box A and Box B) of the split promoter. Transcription was studied in parallel with supercoiled and linear DNA molecules carrying a d(CA/TG) stretch 124‐bp long in front of the tRNAPro gene. The results show the same level of inhibition of Po/III transcription regardless of the topological status of the injected DNA.