Complex sentence: Each of the three zinc fingers recognize three unique base pairs for their DNA-binding sites, which together make the general form NCR CRC CCN (where N is any base and R is a purine).
Split into simpler sentences: Each of the three zinc fingers recognize three unique base pairs in which to bind. Thus the DNA-binding site recognized by these proteins is of the general form NCR CRC CCN (where N is any base and R is a purine).