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.     

Proinsulin cDNAs from the leopard frog, Rana pipiens: evolution of proinsulin processing

We have isolated a proinsulin cDNA from the Amphibian Rana pipiens. The predicted R. pipiens insulin A- and B-chain amino acid sequences differ from that deduced from the closely related Rana catesbeiana at one residue (Asp for Pro at B2). The R. pipiens and Xenopus laevis proinsulin precursor sequences are of identical length, with the amino acid sequences of the mature A- and B-chains being well conserved. The proinsulin C-peptide amino acid sequence is less well conserved between R. pipiens and X. laevis and also differs in length. The R. pipiens C-peptide is shorter than the homologous X. laevis sequence due to a two amino acid residue truncation. The truncation of the R. pipiens C-peptide compensates for a two amino acid residue extension observed at the N-terminal of the A-chains of insulins from Ranid frogs. A change in the site of proinsulin processing can explain both the C-peptide and A-chain length differences. The evolution of the new proinsulin processing site required two amino acid substitutions.