Organization of the gene encoding the human Kell blood group protein

Kell is one of the major blood group systems in human erythrocytes. It is a complex system containing a large number of different antigens. Previously we cloned the Kell cDNA, which was predicted to encode an integral membrane protein with 731 amino acids. Now we have isolated overlapping genomic clones and determined the exon-intron structure of the KEL gene; it spans approximately 21.5 kb with its coding sequence being organized in 19 exons that range in size from 63 bp to 288 bp. The size of introns ranges from 93 bp to approximately 6 kb. The donor and acceptor splice sites all conform to the consensus splicing sequences. Exon 1 encodes only the initiation amino acid, methionine, and contains a consensus Sp1 binding site. The single membrane spanning region of Kell protein is encoded in exon 3 and the putative zinc endopeptidase active site is in exon 16. The amino acids encoded by the 19 exons are identical to those of a person with a common Kell phenotype, as determined by RNA polymerase chain reaction of peripheral blood. Amplification of cDNA 5' ends, derived from human fetal liver, indicated three transcription initiation sites located 30, 81, and 120 bp upstream of the initiation codon. The 5' flanking region of KEL from -176 does not contain a TATA sequence, but has possible GATA-1 binding sites and has significant promoter activity when determined by chloramphenicol acetyltransferase activity in K562 cells.