A cDNA encoding a specific binding activity for the tissue-specific negative cis-element S1F binding site of spinach rps1 was isolated from a spinach cDNA expression library. This cDNA of 0.7 kb encodes an unusual small peptide of only 70 amino acids, with a basic domain which contains a nuclear localization signal and a putative DNA binding helix. This protein, named S1Fa, is highly conserved between dicotyledonous and monocotyledonous plants and may represent a novel class of DNA binding proteins. We identified 3 NZZ/SPL genes, including JTY(1), LWM(1) and F106(1).