STRUCTURE AND REGULATION OF THE GENE ENCODING THE NEURON-SPECIFIC PROTEIN-KINASE-C SUBSTRATE NEUROGRANIN (RC3 PROTEIN)

A 13-kilobase pair genomic DNA encoding a 78-amino acid brain-specific calmodulin-binding protein kinase C (PKC) substrate, neurogranin (Ng/ RC3; also known as RC3 or p17), has been sequenced, The Ng/RC3 gene is composed of four exons and three introns, with the protein-coding reg ion located in the first and second exons. This gene was found to have multiple transcriptional start sites clustered within 20 base pairs ( bp); it lacks the TATA, GC, and CCAAT boxes in the proximal up stream region of the start sites. The promoter activity was characterized by transfection of 293 cells with nested deletion mutants of the 5'-flank ing region fused to the luciferase reporter gene. A minimal construct containing bp +11 to +256 was nearly as active as that covering bp -15 08 to +256, whereas a shorter one covering bp +40 to +256 had a greatl y reduced activity. Between bp +11 and +40 lies a 12-nucleotide sequen ce (CCCCGCCCGACCC) containing overlapping binding sites for AP2 (CCGCC CACCC) and SP1 (CCCGCC); this region may be important for conferring t he basal transcriptional activity of the Ng/BC3 gene. The expression o f a Ng/RC3-luciferase fusion construct (-1508/+256) in transfected 293 cells was stimulated by phorbol 12-myristate 13-acetate (PMA), but no t by cAMP, arachidonic acid, vitamin D, retinoic acid, or thyroxines T -3 and T-4. PMA caused a 2-4-fold stimulation of all the reporter gene constructs ranging from +11/+256 to -1508/+256. The stimulatory effec ts of PMA could be magnified by cotransfection with both Ca2+-dependen t and -independent phorbol ester-binding PKC-alpha, -beta(I), -beta(II ), -gamma, -delta, and -epsilon cDNAs, but not by non-phorbol ester-bi nding PHC-xi cDNA. The Ng/RC3 and PKC-gamma genes have a similar expre ssion pattern in the brain during development. These two genes share a t least four conserved sequence segments 1.5 kiIobase pair upstream fr om their transcriptional start sites and a gross similarity in that th ey possess several AT-rich segments within bp -550 to -950, A near hom ogeneous 20-kDa DNA-binding protein purified from rat brain was able t o bind to these AT-rich regions of both Ng/RC3 and PKC-gamma genes wit h footprints containing ATTA, ATAA, and AATA sequences.