CHARACTERIZATION OF A 190-KILOBASE PAIR DOMAIN OF HUMAN TYPE-I HAIR KERATIN GENES

Polymerase chain reaction-based screening of an arrayed human P1 artif icial chromosome (PAC) library using primer pairs specific for the hum an type I hair keratins hHa3-II or hHaG, led to the isolation of two P AC clones, which covered 190 kilobase pairs (kbp) of genomic DNA and c ontained nine human type I hair keratin genes, one transcribed hair ke ratin pseudogene, as well as one orphan exon, The hair keratin genes a re 4-7 kbp in size, exhibit intergenic distances of 5-8 kbp, and displ ay the same direction of transcription. With one exception, all hair k eratin genes are organized into 7 exons and 6 positionally conserved i ntrons. On the basis of sequence homologies, the genes can be grouped into three subclusters of tandemly arranged genes. One subcluster harb ors the highly related genes hHa1, hHa3-I, hHa3-II, and hHa4. A second subcluster of highly related genes comprises the novel genes hHa7 and hHa8, as well as pseudogene Psi hHaA, while the structurally less rel ated genes hHaG, hHa5, and hHa2 are constituents of the third subclust er. As shown by reverse transcription-polymerase chain reaction, all h air keratin genes, including the pseudogene, are expressed in the huma n hair follicle. The transcribed pseudogene Psi hHaA contains a premat ure stop codon in exon 4 and exhibits aberrant pre-mRNA splicing. Evol utionary tree construction reveals an early divergence of hair keratin genes from cytokeratin genes, followed by the segregation of the gene s into the three subclusters. We suspect that the 190-kbp domain conta ins the entire complement of human type I hair keratin genes.