Additivity of interactions of zinc finger motifs in specific recognition of RNA

Xenopus transcription factor IIIA (TFIIIA) binds 5S rRNA and the 5S rRNA gene, these interactions being mediated by nine zinc fingers. To determine the contribution of each finger to the binding to 5S rRNA we prepared a series of peptides containing different numbers of zinc fingers and analyzed their interactions with RNA. The topography of these complexes was analyzed with the specific RNase and hydroxyl radical footprinting methods. Our results show the direct contribution of each zinc finger (ZF) peptide to the specific recognition of 5S rRNA. These data clearly suggest that total binding of TFIIIA with 5S rRNA is the sum of the specific interactions of the individual zinc fingers with RNA and that they have an additive character.