ISOLATION, SEQUENCE AND EXPRESSION OF THE GENE ENCODING HUMAN KERATIN13

Keratins are a family of highly homologous proteins expressed as pairs of acidic and basic farms which make intermediate filaments in epithe lial cells. Keratin 13 (K13) is the major acidic keratin, which togeth er with K4, its basic partner, is expressed in the suprabasal layers o f non-cornified stratified epithelia. The mechanism which allows mucos al-specific expression of this keratin remains unknown. To provide ins ight into the tissue-specific expression, we have isolated the human K 13 gene by screening a chromosome 17 library with a specific K13 cRNA probe. Sequence analysis of unidirectional deletions produced by trans poson Tn3 has revealed that the gene is 4601 nucleotides long and cont ains seven introns and eight exons. When driven by the CMV promoter, t he gene produced K13 protein in MCF-7 cells, which normally do not exp ress this protein. Two transcription-start sites were identified, the major being at 61 and the minor at 63 nucleotides upstream of ATG. The upstream sequence contained a TATA box and several other putative tra nscription factor binding sites. A single copy of the K13 gene was det ected in the human genome by Southern hybridisation and polymerase cha in reaction. K13 mRNA shows differential expression in cultured kerati nocytes, and in A431 cells the RNA levels remained independent of calc ium concentrations in the culture medium. Characterisation of the huma n K13 gene will facilitate elucidation of the molecular mechanism regu lating K13 expression in mucosal tissues. (C) 1998 Elsevier Science B. V. All rights reserved.