ALLELIC VARIATIONS OF HUMAN KERATIN-K4 AND KERATIN-K5 PROVIDE POLYMORPHIC MARKERS WITHIN THE TYPE-II KERATIN GENE-CLUSTER ON CHROMOSOME-12

To appreciate point mutations in keratin genes as causes for hereditar y epithelial diseases, the normal variation of these gene sequences in the population must be known. Because genetic polymorphism of keratin s at the protein level due to allelic variation has been described for the type II keratins 4 and 5, we have analyzed their corresponding ge nes using single-strand conformation polymorphism gel electrophoresis and sequence analysis of polymerase chain reaction amplified genomic D NA. Although no sequence variations were found in the carboxyl-termina l and rod domains we were able to map the molecular differences among the alleles to their amino-terminal domains. In particular, we have id entified three alleles of keratin 4. Two alleles differed by a nucleot ide transition causing a neutral amino acid substitution (alanine to v aline) and one allele had a 42-bp in-frame deletion corresponding to 1 4 amino acids within the V1 subdomain. Three alleles were also recogni zed for the keratin 5 locus, all being elicited by single nucleotide s ubstitutions. Of these, only one altered the amino acid sequence, repl acing an uncharged (glycine) with a charged (glutamic acid) amino acid in the Hl subdomain. Pedigree analyses in three families showed the a lleles to be inherited as autosomal Mendelian traits. Thus, these norm al alleles of keratins 4 and 5 will provide favorable polymorphic mark ers for linkage analysis directly within the cluster of type II kerati n genes located on chromosome 12q to elucidate the potential involveme nt of these and other keratin genes in disorders of squamous cell diff erentiation.