The hypervariable gene locus PUM, which codes for the tumour associated epithelial mucins, is located on chromosome 1, within the region 1g21–24

A single hypervariable autosomal gene locus, PUM, codes for a family of mucin‐type glycoproteins present in human urine, and in several other normal and malignant tissues of epithelial origin. These mucins can be detected after electrophoresis using a series of monoclonal antibodies that show a pronounced tumour specificity on immunohistochemistry. Using a recently cloned cDNA, pMUC 10, coding for the core protein of the PUM coded mucins, to probe DNA isolated from a series of human‐rodent somatic cell hybrids, we have assigned the PUM locus to chromosome 1. This assignment was confirmed by in situ hybridization of pMUC10 to lymphocyte metaphase chromosomes and the gene was shown to be located within the region 1g21–24. We would like to thank Dr. Ellen Solomon and DrMary Davis for supplying us with unpublished information and material from their hybrids, and Mrs Lynne West for help with karyotype analysis. A. K. is supported by the ICRF.