Figure 1.

Human PRDM9 allele C. A, PRDM9 contains a C-terminal tandem ZF DNA-binding array comprising 13 fingers (allele A; accession no. Q9NQV7) or 14 fingers (allele C; GU216224.1). B, sequence alignment of fourteen C2H2 fingers of PRDM9c with variations at DNA base-interacting positions −1, −4, −7, and −8. For comparison, the four “canonical” positions of the helix are indicated at the bottom of the sequence (20, 21). C, there are two protein-DNA complexes (colored in cyan and green) plus an additional protein molecule (yellow) in the crystallographic asymmetric unit. D, the yellow molecule (Mol C) mediates protein–protein interactions and is not paired with a DNA molecule. Only the first ZF of the unpaired protein is shown, as no electron density was observed for other fingers. E, superimposition of the two protein-DNA complexes. F, structure of ZF8–13 in complex with an allele C-specific DNA molecule.