Evolution of homologous domains of cytoplasmic intermediate filament proteins and lamins

The earliest gene duplications in the evolution of the intermediatefilament proteins created the ancestors of acidic keratins, basic keratins,nonepithelial intermediate filament proteins, and lamins. Biochemistry andfunction of cytoplasmic intermediate filaments differ greatly from those oflamins. Cytoplasmic intermediate filament proteins have a differentcellular location than lamins, form different types of supramolecularstructures, and are missing a protein segment found in lamins; but the datapresented here indicate that the cytoplasmic intermediate filaments do nothave a common ancestor separate from the ancestor of lamins. In thenon-epithelial intermediate filament branch, the ancestor of neurofilamentproteins and the common ancestor of desmin, vimentin, and glial fibrillaryacidic protein (GFAP) diverged first. By evolutionary criteria, theintermediate filament protein recently discovered in neuronal cells doesnot belong to the neurofilament family but is more closely related todesmin, vimentin, and GFAP. Sequences of different sub-domains yielddifferent evolutionary trees, possibly indicating existence of sub-domain-specific functions.