Complete sequence of a hair-like intermediate filament type II keratin gene.

The Intermediate Filament (IF) superfamily comprises several multigene families, of which the two keratin families are the largest. The keratin IF genes are expressed in epithelial tissues in differentiation-specific patterns and recently we reported the sequence and expression of a hair IF type II keratin gene (KRT2.9). Two related genes were present in the cosmid containing KRT2.9 and we have now sequenced one of them and found that it encodes a hair-like IF type II protein (KRT2.13). However, KRT2.13 is not expressed in the hair follicle. Interestingly there is significant sequence homology between introns 1, 5 and 6 of KRT2.13 and KRT2.9 to suggest gene conversion of these regions or possibly conservation of functional sequences.

Avian keratin genes. I. A molecular analysis of the structure and expression of a group of feather keratin genes.

The nucleotide sequence of the four complete chicken feather keratin genes A to D contained in the previously isolated recombinant lambda CFK1 has been determined. All four genes have a very similar structure; each gene encodes a polypeptide of 97 amino acid residues and contains an intron in the 5' non-coding region, 37 base-pairs from the cap site. Comparison of the previously determined feather keratin gene C sequence to genes A, B and D indicates that a high level of gene correction has occurred in the protein coding and 5' non-coding regions, which show more than 90% homology, whereas the intron and 3' non-coding regions are by contrast poorly conserved with one or two exceptions. The dramatic conservation of the 5' non-coding region between the feather keratin sequences and an unrelated but co-expressed gene encoding a histidine-rich protein suggests that this segment may play an important role in transcriptional regulation. In addition, both gene types contain an identically positioned intron in the 5' non-coding region. Northern blots performed using gene-specific probes show that the four characterized genes A to D plus gene E, which is partially contained in the recombinant lambda CFK1, are all expressed in feather tissue from 14-day old chick embryos. In addition, we report that a scale keratin gene (originally isolated from a scale complementary DNA library) is expressed at a low level in the embryonic feather.

Isolation and characterisation of keratin mRNA from the scale epidermis of the embryonic chick.

The keratin polypeptides of the epidermis from the leg scale region of 17-day-old embryonic chicks were extracted as S-carboxymethylated derivatives and characterised by electrophoresis on SDS and pH 9.5 urea gels including a combination of both in two dimensions. Proteins were isolated that gave X-ray diffraction patterns typical of alpha- and beta- (avian feather) keratins. An mRNA fraction was isolated from 17-day-old scale tissue by guanidinium chloride extraction and sucrose gradient fractionation. The mRNA was translated in the wheat germ system to give a major product indistinguishable from the molecular weight class (Mr 14 500) of scale beta-keratin polypeptides. A cDNA library was constructed in pBR322 from a 15 S mRNA subfraction and two recombinant clones were selected by their strong hybridisation to cDNA prepared from the 15 S mRNA. The sequencing of these has yielded details of the relatedness of two scale keratin genes including their 3' untranslated regions. Almost half of the protein sequences of the two homologous scale keratins has been deduced and a notable feature of the scale keratin structure appears to be the presence of at least two sequence domains consisting of 13 amino acid repeats.