Contribution of individual amino acids to the 5S RNA binding activity of the Xenopus zinc finger protein p43.

Xenopus zinc finger protein p43 binds to 5S RNA in immature oocytes to form a 42S ribonucleoprotein storage particle. To determine the role of individual zinc fingers of the protein in this RNA binding activity, a series of deletion and substitution mutants of p43 were constructed. The effects of the various mutations on the RNA binding activity of p43 were determined using a quantitative equilibrium binding assay. The results indicate that zinc fingers 1 and 4 of p43 are essential for the binding of the protein to 5S RNA. In the case of finger 1, four amino acids key to RNA binding are found on the same face of the alpha-helix, while in the case of finger 4, two key residues are clustered at the start of the alpha-helix. The similarities and differences in the mechanisms by which fingers 1 and 4 of p43 interact with 5S RNA are compared to the interaction of the zinc fingers of Xenopus transcription factor IIIA with 5S RNA.