Sequence-specific recognition of a repetitive DNA element by a C2H2 zinc-finger protein in Xenopus

XFG 20-1 is one of several hundred C2H2-type zinc finger proteins of unknown biological function in Xenopus. Affinity selection of genomic DNA fragments identifies a 54-bp consensus sequence with high affinity for the XFG 20-1 protein. This sequence is part of a conserved inverted repeat in REM-1, a 0.5-kb repetitive, dispersed genomic DNA element. This finding indicates a possible link between the non-conserved nature of a large subgroup of DNA-binding C2H2 zinc finger proteins and the non-conserved nature of putative genomic target sequences. The 19 zinc finger modules of XFG 20-1 are organized in three structurally distinct groups. Of these, only the first and third ones are required and are sufficient for high-affinity DNA binding. The finding that removal of five internal zinc finger units does not alter the DNase I protection pattern of the complex formed is indicative of a high degree of structural flexibility for linear arrays of zinc fingers, which we imagine to adopt a more rigid structure only upon interaction with their nucleic acid partner molecules.