A new family of DNA binding proteins includes putative transcriptional regulators of theAntirrhinum majus floral meristem identity geneSQUAMOSA

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Abstract
Several sites of nuclear protein interaction within the promoter region of theAntirrhinum majus floral meristem identity geneSQUAMOSA were detected using an electrophoretic mobility shift assay. One of these sites displayed a particularly clear interaction with nuclear protein extracted from inflorescences but not with nuclear protein extracted from young, non-flowering plants. This site could thus represent a binding motif for a transcriptional activator. A South-western screen of an inflorescence cDNA expression library resulted in the isolation of several cDNAs representing two different genes namedSBP1 andSBP2 (forSQUAMOSA-pROMOTERBINDINGP ROTEIN gene 1 and 2). Both genes encode highly similar protein domains which were found to be necessary and sufficient for binding DNA in a sequence-specific manner. This DNA-binding domain showed no similarity to known proteins in the databases. However, it is characteristic for a small family of gene products inA. majus and other plant species. Expression ofSBP1 and2 is developmentally regulated and their transcriptional activation precedes that ofSQUAMOSA. The data presented support the idea that members of the newly identifiedSBP gene family function as transcription factors involved in the control of early flower development.