InterPro domain: IPR004333

SBP (for SQUAMOSA-pROMOTER BINDING PROTEIN) domain is a sequence specific DNA-binding domain found in plant proteins [ 1 ]. Members of family probably function as transcription factors involved in the control of early flower development [ 2 ]. They share a highly conserved DNA-binding domain that contains two zinc-binding sites. Among the 11 possible ligands for the zinc atoms that are conserved in the SBP zinc finger, only 8 are used. The SBP zinc finger follows the general pattern C-x4-C-x16-C-x2-[HC]-x15-C-x2-C-x3-H-x11-C. Three other histidines are well conserved but not involved in zinc binding [ 2 , 2 ].

In vitro experiments show that the SBP zinc finger preferentially binds theconsensus sequence -TNCGTACAA- [ 3 ]. However, little is known of the physiological functions of these putative transcriptional regulators beyond their ability to bind DNA.

The solution structure of the SBP zinc finger has been solved[ 4 ]. The first four Cys or His coordinate one zinc ion and the last four coordinate the other. It can be viewed as two structural subdomains, each subdomain containing a single zinc-binding pocket. The N-terminal subdomain consists of two short alpha helices whereas the C-terminal one contains a three-stranded antiparallel beta-sheet.

1. A new family of DNA binding proteins includes putative transcriptional regulators of the Antirrhinum majus floral meristem identity gene SQUAMOSA. Mol. Gen. Genet. 250, 7-16
2. A novel zinc-binding motif revealed by solution structures of DNA-binding domains of Arabidopsis SBP-family transcription factors. J. Mol. Biol. 337, 49-63
3. Molecular characterisation of the Arabidopsis SBP-box genes. Gene 237, 91-104