THE SPECIFICITY OF HOMEOTIC GENE-FUNCTION

How transcription factors achieve their in vivo specificities is a fun damental question in biology. For the Homeotic Complex (HOM/Hox) famil y of homeoproteins, specificity in vive is likely to be in part determ ined by subtle differences in the DNA binding properties inherent in t hese proteins. Some of these differences in DNA binding are due to seq uence differences in the N-terminal arms of HOM/Hox homeodomains. Evid ence also exists to suggest that cofactors can modify HOM/Hox function by cooperative DNA binding interactions. The Drosophila homeoprotein extradenticle (exd) is likely to be one such cofactor. In HOM/Hox prot eins, both the conserved 'YPWM' peptide motif and the homeodomain are important for interacting with exd. Although exd provides part of the answer as to how specificity is achieved, there may be additional cofa ctors and mechanisms that have yet to be identified.