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The INT6 gene is a common integration site for the mouse mammary tumor virus in mouse mammary tumors. We have determined that the human homolog of INT6 is located on chromosome region 8q22-q23. A processed INT6 pseudogene is located on chromosome 6q. INT6 is composed of 13 exons that span 45 kb of genomic DNA. The deduced amino acid sequence of the gene product is identical to the mouse protein and contains three potential translation start signals. We have examined 100 primary breast carcinoma DNAs for evidence of genetic alteration affecting INT6. Loss of heterozyosity (LOH) was detected in 11 of 39 (28%) of the tumor samples informative for a polymorphic sequence in intron 7 of INT6. Since single-strand conformation and hybrid mismatch analysis of the remaining allele in these tumor DNAs failed to detect any mutations, we conclude that the target gene for LOH must be closely linked to INT6.

A cDNA corresponding to the beta-subunit of the human fibronectin receptor (beta-FNR) was used as a probe in Southern blot analysis of mouse/human somatic cell hybrid DNAs and in in situ hybridization to metaphase chromosomes. The beta-FNR cDNA detects sequences present on human chromosome 10 as well as recognizing homologous sequences in the genome of the mouse parent of the somatic cell hybrids. In situ hybridization refined the localization of human sequences reacting with the beta-FNR cDNA to 10p11.2. The A-1A5 monoclonal antibody which recognizes the beta-subunit of the fibronectin receptor on the cell surface was used to confirm that the sequences present on chromosome 10 correspond to those required for expression of beta-FNR.