CHARACTERIZATION OF THE 5 S RNA-BINDING ACTIVITY OF XENOPUS ZINC-FINGER PROTEIN P43

One major component of the Xenopus 42 S ribonucleoprotein (RNP) storag e particle is the p43 protein. The 5 S RNA binding protein is structur ally similar to TFIIIA, containing nine zinc;finger domains. The RNA b inding properties of recombinant p43 were characterized using a nitroc ellulose filter binding assay: The experimental conditions necessary f or in vitro p43-5 S RNA complex formation include: pH 7.5, 0.1 M KCl a nd incubation at 22 degrees C. Under these conditions, the protein bin ds to Xenopus oocyte 5 S RNA with an apparent association constant of 1.61(+/-0.12)x10(9) M(-1). A series of mutations in 5 S RNA were used to determine which sequence and structural features of the 5 S RNA are required for high affinity binding of p43. The primary contact points for p43 include the sequences and structures of stems II, V and loop D of the 5 S RNA. Although p43 and TFIIIA are structurally similar and are both relatively insensitive to mutations in the 5 S RNA, they do require different features of the 5 S RNA molecule for high affinity b inding.