A finger protein structurally similar to TFIIIA that binds exclusively to 5S RNA in Xenopus

A 5S RNA binding protein (p43) in Xenopus is a major constituent of oocytes and comprises part of a 42S ribonucleoprotein storage particle. We have cloned and sequenced p43 cDNA from X. laevis and X. borealis as well as the cDNA for X. borealis TFIIIA. Like TFIIIA, p43 has nine zinc fingers, seven of which are exactly the same size as their counterparts in TFIIIA. Amino acid homology between the two proteins is restricted mainly to conserved residues characteristic of zinc fingers. In contrast to TFIIIA, which binds specifically to both 5S RNA and 5S RNA genes, p43 binds exclusively to 5S RNA.     

Second-order repeats in Xenopus laevis finger proteins

The primary structure of 342 finger repeats encoded in 42 different cDNA clones isolated from Xenopus laevis oocyte and gastrula cDNA libraries has been determined. Comparative sequence analysis of the predicted protein sequences results in a consensus repeat sequence that has an extended conserved segment of 16 amino acid residues, including the evolutionary conserved H/C link element, connected to a highly variable segment that is located in the finger loop region. Groups of tandem finger repeats are found to be organized in distinct higher-order structural units, with a pair of mutually distinct fingers being the most frequently observed second-order repeat unit. Structural features observed are discussed in respect to existing models for Zn finger structure and function.