CONSERVATION OF THE RD-BF-C2 ORGANIZATION IN THE PIG MHC CLASS-III REGION - MAPPING AND CLONING OF THE PIG RD GENE

The RD gene, named after the arginine (R) and aspartic acid (D) repeat in the central part of its protein, was initially mapped in the mouse H-2S subregion between C4 and BF, It was later mapped in the same pos ition in the human MHC and here we show it is also conserved in the pi g MHC class III region, close to the complement BF gene. A pig RD geno mic clone was isolated from a h-phage library. Hybridizations on genom ic DNA separated with pulsed field gel electrophoresis identified comm on 220 kb NruI, 130 kb EagI and 200 kb MluI bands for RD, BF and C2. T he RD gene has also a 17 kb KpnI and 11 kb SacI fragment in common wit h BF but not with C2. The close linkage of the RD and BF genes was fur ther established by hybridization of BF to a genomic lambda-phage clon e also containing the RD gene. This genomic RD clone overlaps with a h -phage clone previously isolated and containing the complete BF gene a nd the 3' part of C2. The distance between RD and BF is about 6 kb, Th e junction between the two complement genes BF and C2 was sequenced an d the BF 5' promoter region, overlapping the 3' noncoding region of C2 , was compared with that of the human BF promoter. The overall homolog y was about 80% and all but one identified promoter elements were foun d in the same position in both genes. The results obtained demonstrate the RD-BF-C2 organization is strongly conserved between human, mouse and pig. No polymorphisms were detected in either the RD gene or in th e BF promoter region using polymerase chain reaction and restriction f ragment polymorphism analysis.