RESUMO
The Drosophila gene snail (sna) which encodes a zinc finger protein is essential for dorsal-ventral pattern formation in the developing embryo. We have defined a repertoire of SNAIL (SNA) binding sites using recombinant SNA proteins to select specific binding sequences from a pool of random sequence nucleotides. The bound sequences which were selected by multiple rounds of gel retardation and amplification by the polymerase chain reaction (PCR) were subsequently cloned and sequenced. The consensus sequence, 5'G/A A/t G/A A CAGGTG C/t A C 3', with a highly conserved core of 6 bases, CAGGTG, shares no significant homology with known binding sequences of other Drosophila zinc finger proteins. However, the CAGGTG core is identical to the core motif of aHLH (helix-loop-helix) binding sites. The strongest SNA binding is obtained with sequences containing this core motif whereas reduced binding is seen for sequences with canonical CANNTG HLH motifs. Interestingly, SNA binding is detected in the promoter region of the snail gene. Transient expression in co-transfection experiments using a SNA binding element (SBE) linked to a heterologous promoter indicates that SNA has the ability to function as a transcription activator.
