Highly cooperative homodimerization is a conserved property of neural POU proteins

POU-domain proteins have been shown to play important roles in the developm ent of the nervous, endocrine, and immune systems. However, the distinctive DNA recognition properties of the six major POU subclasses have not been w ell defined. Here, we have used random oligonucleotide selection and compet itive binding assays to determine the optimal DNA recognition elements for the POU-III and POU-VI protein classes, represented by Brn-2 and Brn-5, res pectively. The optimal Brn-5 consensus binding sequence GCATAA(T/A)TTAT str ongly resembles that previously determined for the POU-IV (Brn-3) class, wh ereas Brn-2 exhibits highest affinity for non-octamer sites of the form ATG (A/C)AT(A/T)(0-2) ATTNAT and for octamer sites that contain a full associat ed heptamer sequence. Brn-2, Brn-3.0, and their invertebrate homologues all . exhibit highly cooperative homodimerization on the Brn-2 consensus sequen ce, demonstrating that cooperative dimerization is a general property of th ese neural POU proteins. However, modified sites to which Brn-2 binds only as a monomer mediate the transcriptional effects of Brn-2 better than the c onsensus sequence, demonstrating that dimerization on these sites diminishe s the transactivation ability of the protein, Together with the findings of our prior studies these data greatly facilitate the identification of func tional POU recognition elements in the regulatory regions of neural genes.