The IRTA locus spans 300 kb in a chromosome segment containing Fc receptors and genes identified through analysis of chromosomal translocations in B-cell malignancy.

The top line shows a portion of chromosome 1q21, indicating the positions of selected genes and their respective genomic sequence accession numbers, according to the working draft sequence of the Human Genome Sequencing Project, as of January 21, 2001. The centromere is to the left. The position of MUC-1 (EMA) is based upon the Celera human genome sequence.48 The second line shows a magnification of the indicated region of line 1, with the IRTA genes depicted as arrows in the direction of transcription under their respective sequence contigs. The third line shows the intron/exon structure of each IRTA gene, with filled boxes indicating coding exons and open boxes indicating noncoding regions of mRNA. The position of the chromosomal breakpoint in the initial cell line analyzed is indicated by an arrow. Scale bars are shown on the left for the lower 2 lines.