cDNA sequencing of nuclear lamins A and C reveals primary and secondary structural homology to intermediate filament proteins.

TLDR

Lamins A and C share extensive homology with intermediate filament proteins, and lamin A contains an 82‑residue C‑terminal extension homologous to keratin domains. Sequence analysis shows that lamin A and C are nearly identical except for a 9‑kDa tail unique to A, and both contain a ~360‑residue alpha‑helical rod domain homologous to intermediate filament proteins, though the lamin domain is 14% larger, implying a role in nuclear lamina assembly.

Abstract

The amino acid sequences deduced from cDNA clones of human lamin A and lamin C show identity between these two lamins except for an extra 9.0-kDa carboxyl-terminal tail that is present only in lamin A. Both lamins A and C contain an alpha-helical domain of approximately 360 residues that shows striking homology to a corresponding alpha-helical rod domain that is the structural hallmark of all intermediate filament proteins. However, the lamin alpha-helical domain is 14% larger than that of the intermediate filament proteins. In addition to the extensive homology to intermediate filament proteins as reported [McKeon, F., Kirschner, M. & Caput, D. (1986) Nature (London) 319, 463-468], a different 82-amino acid residue stretch at the carboxyl terminus of lamin A has been deduced and verified by amino acid sequencing. This region contains sequence homology to amino- and carboxylterminal domains of type I and type II epidermal keratins. Implications of the presence of these and other domains in lamins A and C for the assembly of the nuclear lamina are discussed.