ZINC(II) IONS SELECTIVELY INTERACT WITH DNA-SEQUENCES PRESENT AT THE TFIIIA BINDING-SITE OF THE XENOPUS 5S-RNA GENE

It has been known for some time that zinc, as well as most transition metal ions, is capable of binding to the DNA bases, However, little is known about the presence and distribution of metal binding sites alon g naturally occurring genomic DNA molecules, In this paper, the intera ction of zinc with the Xenopus 5S-RNA gene has been studied and severa l metal binding sites have been identified on the basis of the changes in chemical reactivity observed in the presence of the metal, The str ongest zinc-binding sites of the Xenopus 5S-RNA gene correspond to GGG trinucleotide repeats, Some GG dinucleotides also show a significant affinity for zinc, Interestingly, the binding site for TFIIIA, a zinc- finger transcription factor, contains several sites with strong zinc a ffinity, In particular, a TGGGA sequence which is essential for the bi nding of TFIIIA shows the strongest affinity for zinc, The conformatio nal properties of this DNA sequence, together with the high electroneg ative potential of GGG runs, is likely to determine its strong affinit y for zinc, The possible biological relevance of these results is disc ussed.