Zinc fingers are sticking together

It is estimated that there are 500 zinc-finger proteins encoded in the yeast genome and that perhaps 1% of all mammalian genes encode zinc fingers. Why are these protein modules so abundant? Zinc fingers are known as DNA-binding motifs; sequential arrays of zinc fingers arranged in different combinations can recognize a huge range of DNA sequences, and interactions with both RNA and with DNA-RNA hybrids have also been observed. But recent reports suggest that there may be an additional explanation for the prevalence of zinc-finger proteins - they can mediate protein-protein interactions. The realization that zinc fingers can interact with each other and with other proteins may help explain not only why there are so many finger proteins, but also why individual proteins often have so many fingers. In particular, it may explain the presence of fingers that do not bind DNA. There are several different types of fingers, categorized by the nature and spacing of their zinc-chelating residues. In this article we will focus mainly on the classical zinc fingers (referred to as CCHH, TFIIIA or Krueppel-like fingers) and the GATA-like CCCC fingers.