Maf transcription factors form a distinct family of the basic leucine zipper (bZip) transcription factors. The Maf family is divided into two subclasses, large Mafs (c-maf, mafB, and mafA/L-maf, Nrl) and small Mafs (MafF, MafK and MafG). Both subclasses contain leucine-zipper motifs, which allow homodimerisation as well as heterodimerisation with a variety of other bZip proteins. In contrast to the small Mafs, the large Maf proteins contain a transactivator domain in their amino terminus.Neural retina-specific leucine zipper protein (Nrl) is a member of the Maf family of transcription factors that regulates the expression of rod-specific genes, including rhodopsin [, , ]. Mutations in Nrl cause retinitis pigmentosa 27 (RP27), which is a retinal dystrophy belonging to the group of pigmentary retinopathies [, ], and retinal degeneration autosomal recessive clumped pigment type (RDCP), which is a retinopathy characterised by night blindness since early childhood, consistent with a severe reduction in rod function [].
The NRL (for NPH3/RPT2-Like) family is formed by signaling molecules specificto higher plants. Several regions of sequence and predicted structuralconservation define members of the NRL family, with three domains being mostnotable: an N-terminal BTB domain, a centrally located NPH3domain, and a C-terminal coiled coil domain. The function of the NPH3 domainis not yet known [, , , , , , , ].Some proteins known to contain a NPH3 domain include:Arabidopsis non-phototropic hypocotyl 3 (NPH3), may function as an adapteror scaffold protein in plants.Arabidopsis root-phototropisme 2 (RPT2), a signal transducer involved inphototropic response and stomatal opening in association with phototropin 1(phot1).Oriza coleoptile phototropism 1 (CPT1), the rice ortholog of NPH3. It isrequired for phototropism of coleoptiles and lateral translocation ofauxin.This entry represents the NPH3 domain.
The NRL (for NPH3/RPT2-Like) family is formed by signaling molecules specificto higher plants. Several regions of sequence and predicted structuralconservation define members of the NRL family, with three domains being mostnotable: an N-terminal BTB domain, a centrally located NPH3domain, and a C-terminal coiled coil domain. The function of the NPH3 domainis not yet known [, , , , , , , ].Root phototropism protein 3 (RPT3), also known as nonphototropic hypocotyl 3 (NPH3), and root phototropism 2 (RPT2) () represent the founding members of a novel plant-specific family []. Three domains define the members of this family: an N-terminal BTB (broad complex, tramtrack, bric a brac) domain (), a centrally located NPH3 domain (), and a C-terminal coiled-coil domain.NPH3 assembles with CUL3 to form a E3 complex that ubiquitinates phototropin 1 (phot1) and modulates phototropic responsiveness [, ]. NPH3 is necessary for root and hypocotyl phototropisms, but not for the regulation of stomata opening or chloroplast relocation []. Coleoptile phototropism protein 1 (CPT1) is a rice orthologue of Arabidopsis NPH3 also required for phototropism []. This entry also includes DOT3 (AT5G10250) that is involved in shoot and primary root growth; DOT3 mutants produce an aberrant parallel venation pattern in juvenile leaves [].
