The Sequence of the Human Epidermal 58-kD (#5) Type II Keratin Reveals an Absence of 5′ Upstream Sequence Conservation between Coexpressed Epidermal Keratins

We report the isolation and sequencing of cDNA and genomic clones encoding the complete sequence of the human 58-kD epidermal keratin (#5). The sequence specifies a protein of 62,471 daltons that contains a central α-helical segment capable of forming a coiled-coil structure flanked by regions that are not α-helical. A comparison of the primary sequence with the known sequences of other intermediate filament proteins reveals many common motifs. The 58-kD keratin is highly similar to other type II keratins and less similar to type I keratins and other intermediate filament proteins. The 58-kD keratin is regulated by retinoids in several tissues and is one of four keratins abundantly expressed in epidermal keratinocytes, where it may be important in maintaining structural integrity of the integument. A comparison of the keratin 5 sequence with coexpressed keratin 14 reveals an absence of sequence conservation in regulatory regions and suggests that common sequence elements may not be necessary for coordinate expression of type I and type II keratin partners. Interestingly, keratin 5 contains only one region weakly resembling the SV40 enhancer-like sequence found in some other keratins indicating that this sequence motif may not be necessary for regulation or abundant expression of all epidermal keratins.