The gene organization of human TAPL (TAP-like, ABCB9) was determined. The TAPL gene consists of 12 exons including the first non-coding exon on human chromosome 12q23.34. Three alternative splicing variants of the 12th exon have been identified by 3'RACE using RNA from human cell lines and isolated lymphocytes. As expected from the similarity of the amino acid sequences of TAP1, TAP2, and TAPL, the intron insertion points in these three genes are essentially the same. However, the TAP2 and TAPL genes are closely related, since each has common non-coding exon and splicing isoforms. The novel splicing variants of TAPL termed 12B and 12C have shorter carboxyl terminal amino acid sequences than 12A, reportedly a conserved isoform in rodents and human. The proximal promoter region of the TAPL gene lacks a canonical TATA-box but contains several GC-box elements. The 60 bp upstream sequence containing two GC-boxes from the human TAPL transcriptional start site confers basal promoter activity. (C) 2003 Elsevier Inc. All rights reserved.