Note: this site last updated in 2006
An article from "The Molecules of HIV" (c) Dan Stowell
A zinc finger is a structure that can occur in proteins (particularly ones which bind to DNA or RNA). A string of amino acids folded back on itself forms a "finger-shaped" bit of protein. At the base of the "finger" are two cystine and two histidine amino acids, which bind with a single zinc ion to hold the structure together.
Zinc fingers occur in various proteins in nature. They're also particularly interesting to scientists because they can be used to recognise a particular short sequence of DNA code.