Chromosomal localization of three human genes coding for A15, L6, and S5.7 (TAPA1): all members of the transmembrane 4 superfamily of proteins.

The A15, L6, and S5.7(TAPA1) proteins are members of the transmembrane 4 superfamily (TM4SF). The A15 is expressed in immature human T cells and in the human brain. The MXS1(CCG-B7) gene which codes for A15 contains triplet nucleotide repeats which have been associated with neuropsychiatric diseases such as Huntington's chorea, fragile X syndrome, and myotonic dystrophy. The L6 antigen is mainly expressed in lung, breast, colon, ovarian carcinomas, and healthy epithelial tissue in humans. The S5.7(TAPA1) antigen is expressed in most human cell lines and is shown to be associated with B-cell surface molecules CD19 and Leu-13. In this study we have used interspecies specific somatic cell hybrids and human-specific cDNA probes to localize the A15 (MXS1), L6 (M3S1), and TAPA1 genes to Xq11, 3q21-25, and 11p15.5, respectively.