COLOCALIZATION OF THE KETOHEXOKINASE AND GLUCOKINASE REGULATOR GENES TO A 500-KB REGION OF CHROMOSOME 2P23

The glucokinase regulator (GCKR) is a 65-kDa protein that inhibits glu cokinase (hexokinase TV) in liver and pancreatic islet. The role of gl ucokinase (GCK) as pancreatic beta cell glucose sensor and the finding of GCK mutations in maturity onset diabetes of the young (MODY) sugge st GCKR as a further candidate gene for type 2 diabetes. The inhibitio n of GCK by GCKR is relieved by the binding of fructose-1-phosphate (F -1-P) to GCKR. F-1-P is the end product of ketohexokinase (KHK, fructo kinase), which, like GCK and GCKR, is present in both liver and pancre atic islet. KHK is the first enzyme of the specialized pathway that ca tabolizes dietary fructose. We have isolated genomic clones containing the human GCKR and KHK genes. By fluorescent in situ hybridization (F ISH), KHK maps to Chromosome (Chr) 2p23.2-23.3, a new assignment corro borated by somatic cell hybrid analysis. The localization of GCKR, ori ginally reported by others as 2p22.3, has been reassessed by high-reso lution FISH, indicating that, like KHK, GCKR maps to 2p23.2-23.3. The proximity of GCKR and KHK was further demonstrated both by two-color i nterphase FISH, which suggests that the two genes lie within 500 kb of each other, and by analysis of overlapping YAC and P1 clones spanning the interval between GCKR and KHK. A new microsatellite polymorphism was used to place the GCKR-KHK. locus between D2S305 and D2S165 on the genetic map. The co-localization of these two metabolically connected genes has implications for the interpretation of linkage or allele as sociation studies in type 2 diabetes. It also raises the possibility o f coordinate regulation of GCKR and KHK by common cis-acting regulator y elements.