INTERACTION OF THE RNA-BINDING FINGERS OF XENOPUS TRANSCRIPTION FACTOR IIIA WITH SPECIFIC REGIONS OF 5-S RIBOSOMAL-RNA

Zinc fingers 4 to 7 of Xenopus transcription factor IIIA (TFIIIA) repr esent the minimal polypeptide necessary for high-affinity binding to 5 S RNA. Mutations covering the entire 5 S RNA structure have been comp ared for their effects on the binding affinity of full-length TFIIIA a nd a polypeptide consisting of fingers 4 to 7 of TFIIIA (zf4-7). In ad dition, ribonuclease footprinting was used to compare the binding site s of TFIIIA and zf4-7 on 5 S RNA. The consistency between the data obt ained from these two approaches provided a clear indication that zinc fingers 4 to 7 of TFIIIA bind to a central core region on the 5 S RNA molecule consisting of loop B/helix II/loop A/helix V/region E. This i nformation was used to design a truncated 75-nucleotide-long RNA molec uler that retains high affinity for zf4-7. Therefore, we conclude that the specific interaction of TFIIIA with 5 S RNA can be represented by a complex formed between a four zinc finger polypeptide and a truncat ed 5 S RNA molecule.