Gene structure and protein topology. (A) Genomic organization of the AtMRP6 gene (At3g13090) deduced from the cDNA. The 9 exons are represented by blue boxes. Triangles indicate the localization of T-DNA insertions in the three different insertion lines investigated. Position of the two nucleotide-binding domains is symbolized by the NBD boxes. The right and left flanking regions (AtMRP3, At3g13100 and AtMRP7, At3g13080) are represented by their intergenic distance. (B) Transmembrane domains were determined using the criteria proposed for classical membrane proteins . It could be possible for the protein to exhibit an internal symmetry consistent with an even number of transmembrane helices, six in each half and a TMD0 of at least three transmembrane spans at the end terminal part. The X-Axis represents the amino-acids position along the protein sequence. Walker A domains are represented in both halves by the dotted lines.