Characterization of bovine keratin genes: similarities of exon patterns in genes coding for different keratins.

Abstract

Four different genomic clones which contain the genes coding for epidermal keratins Ia (mol. wt. approximately 68 000), Ib (68 000), III (60 000) and VIb (54 500) have been selected using cDNA probes and identified by hybrid‐selection translation. The genes vary considerably in length, primarily due to differences in intron sizes: keratin Ia, 9.3 kb (approximately 2.55 kb total exons); keratin Ib, 6.0 kb (2.25 kb exons); keratin III, 6.0 kb (2.2 kb exons); keratin VIb, 4.4 kb (1.85 kb exons). The genes for all three representatives of the basic (type II) cytokeratin subfamily, i.e., keratins Ia, Ib and III, contain eight introns of variable sizes (0.1‐1.8 kb) and their exon patterns are very similar. The gene coding for keratin VIb, a representative of the acidic (type I) subfamily, contains seven introns, and the size pattern of its five innermost exons closely resembles that of the genes of the type II keratins. Most of the introns are located in regions coding for the alpha‐helical cores of these proteins. Mapping of the intron positions by the S1 nuclease technique and sequencing of some exon‐intron boundaries has revealed that some of the introns of all four keratin genes have similar positions to each other and to those of the hamster vimentin gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Three tightly linked genes encoding human type I keratins: conservation of sequence in the 5'-untranslated leader and 5'-upstream regions of coexpressed keratin genes.

“…The possibility of differential usage of exonintron splice junctions within the internal intron sequences of a keratin hnRNA transcript is highly unlikely, since a strong evolutionary pressure exists against shifting these intron positions (26,34,36,37,67). Two additional lines of evidence now indicate that K13 and K16 cannot arise from differential processing of the 3' or 5' external exon-intron junctions of the heterogeneous nuclear RNA transcript of gene C: (i) a unique subcloned prQbe for the known exon VIII of gene C selects only the mRNA for K17 and (ii) none of the mRNAs from pultured human epidermal cells hybridizes with sequences located 3' to the known polyadenylation signal of gene C and 5' to the approximate start of gene D. Although we have not yet ruled out the possibility that other keratin mRNAs expressed developmentally or in other tissues might arise from tissue-specific processing of the gene C transcript, this is unlikely due to the more distant relation of the mRNAs for nonepidermal type I keratins (30).…”

Transgenic mice as a model to study the role of TGF-beta-related molecules in hair follicles.

“…The genomic organization of the bovine cytokeratins III and IV* (Lehnert et al 1984;Blessing et al 1987) was reconstructed in a pBR322 {Bolivar et al 1977) derivative that consists of the 1989-bp NdeI-AatII fragment containing the origin of replication and the ampicillin resistance gene. A polylinker with the following restriction enzyme recognition sites has been introduced to facilitate the reconstruction of the genomic organization of these cytokeratin genes, as well as the excision of these constructs, to separate them from vector sequences for embryo injection:…”

Clustered arrangement of keratin intermediate filament genes.

“…No (Fig. 4) (32) and the postulated intron/exon junctions occur in the same positions relative to the protein sequence as determined for nine IF genes (9)(10)(11)(12)(13)34).…”

“…Intermediate filaments (IF) [10][11][12][13][14][15][16][17][18][19][20] proteins, which are encoded by a similar number of genes (5-7). Yet, from this large repertoire of type I and type II genes only a few, typically one coordinately expressed pair, seem to be expressed in any given epithelial phenotype (6,8).…”

“…A comparison of coordinately expressed genes may indicate regulatory sequences that are involved in this coupled expression and it is possible that these coordinately expressed genes are linked in the genome. Recently, individual type I and type II keratin genes were isolated from human (9)(10)(11), mouse (12), and bovine (13) genomic libraries, but it is not known whether the type I and type II genes are linked or, indeed, if there is any linkage within the two gene families.…”