GENOMIC ORGANIZATION OF THE HUMAN DDX13 GENE LOCATED BETWEEN RD AND RP1 IN THE CLASS-III MHC COMPLEX

Recently we cloned a novel human cDNA homologous to yeast SKI2, report ed a partial cDNA sequence, and mapped the gene to human chromosome 6p 21. (Lee et al., 1995), It was a member of the DEAD/DExH family gene w ith seven conserved helicase domains; thus, it was named DDX13 consequ ently. We determined the complete genomic organization of the DDX13 ge ne. It consisted of 28 exons distributed over 11 kb of genomic DNA. An Alu element was present in introns 17 and 18, respectively. The major transcription start site was located 390 bp upstream from the transla tion initiation codon. The DDX13 gene was located in the class III reg ion of the MHC between the genes coding for two other nuclear proteins , RD and RP1. The RD and DDX13 genes were oppositely oriented, and the ir first exons were overlapped, The distance between their first methi onine codons was only 745 bp. It was of note that DDX13 and RD are in such proximity that their 5' regulatory regions overlap. The RP1 gene was located immediately downstream from the DDX13 gene in the same tra nscriptional orientation, and the distance between the stop codon of D DX13 and the translation initiation codon of RP1 was 2,272 bp.