THE PREDICTED AMINO-ACID-SEQUENCE OF ALPHA-INTERNEXIN IS THAT OF A NOVEL NEURONAL INTERMEDIATE FILAMENT PROTEIN

Our laboratory recently isolated and began to characterize a 66 kd rat brain cytoskeletal protein, dubbed α-internexin for its interactions in vitro with several other cytoskeletal proteins. Although α-internexin bore several of the characteristics of intermediate filament (IF) proteins, including the recognition by an antibody reactive with all IF proteins, it did not polymerize into 10 nm filaments under the conditions tested. Here we show that the predicted amino acid sequence of a cDNA encoding α-internexin shows the latter to be an IF protein, probably most closely related to the neurofilament proteins. Northern blotting shows that α-internexin expression is brain specific, and that rat brain α-internexin mRNA levels are maximal prior to birth and decline into adulthood, while the converse is seen for NF-L, the low molecular weight neurofilament subunit, suggesting that these two proteins play different roles in the developing brain.