DNA-BINDING SPECIFICITY OF THE S8-HOMEODOMAIN

The murine S8 homeobox gene is expressed in a mesenchyme-specific patt ern in embryos. as well as in mesodermal cell lines. The S8 homeodomai n is overall similar to paired type homeodomains. but at position 50, which is crucial for specific DNA recognition, it contains a Gln. as i s found in Antennapedia (Antp)-type homeodomains. We determined the DN A-binding specificity of the purified S8 homeodomain by in vitro selec tion of random oligonucleotides. The resulting 11-bp consensus binding site, ANC/TC/TAATTAA/GC resembles, but subtly differs from, the recog nition sequences of Antp-type homeodomains. Equilibrium binding consta nts of down to 6.0 x 1 0(-10) M were found for binding of the S8 homeo domain to selected oligonucleotides. Using specific antibodies and an oligonucleotide containing an S8-site, we detected by band-shift two a bundant DNA binding activities in mesodermal cell lines that correspon d to S8 and two more that correspond to its close relative MHox. These S8 protein forms are differentially expressed in retinoic acid-treate d P19 EC cells.