Abstract
The primary structure of the major 60-kDa squid low molecular mass neurofilament protein (NF60) and a related 70-kDa neurofilament protein have been determined from cDNA clones isolated from a squid brain cDNA library. Structural analysis suggests that the squid NF60 and NF70 neurofilament genes and proteins are remarkably distinct from vertebrate neuronal intermediate filaments characterized previously. Both proteins are encoded on mRNAs generated by alternative RNA processing of the primary transcript of a single gene. Among the known intermediate filament proteins, NF60 and NF70 neurofilament proteins show highest similarity to an epithelial intermediate filament protein from Helix pomatia, a gastropod mollusk, and are less similar to vertebrate neurofilaments. The length of the alpha-helical rod domain in the NF60 and NF70 proteins was reminiscent of the vertebrate nuclear lamins, 6 heptads longer than is found in all known vertebrate cytoplasmic intermediate filaments, in particular the vertebrate neurofilaments. These distinct structural properties suggest that the vertebrate and invertebrate low molecular weight neurofilaments evolved independently from primordial intermediate filament proteins.
Highlights
From the Laboratoryof Neurochemistry, National Instituteof Neurological Disorders and Stroke, Bethesda, Maryland20892 and the Marine Biological Laboratory, Woods Hole, Massachusetts 02543
Using a cDNA probe [15] from mouse NF-L for low stringency hybridization screenings of a squid brain cDNA library, we found clones representing the 60-kDa (NF60) and a separat7e0-kDa neurofilament protein (NF70)
We describe the cloning and sequencing of cDNAs representing two neurofilament proteins from cDNA libraries made from the optic lobe of the squid, Loligo pealei
Summary
From the Laboratoryof Neurochemistry, National Instituteof Neurological Disorders and Stroke, Bethesda, Maryland20892 and the Marine Biological Laboratory, Woods Hole, Massachusetts 02543. Structural analysis suggests that the squid NF60 and NF70 neurofilament genes and proteins are remarkablydistinct from vertebrate neuronal intermediate filaments characterized previously. Two clear lamins, 6 heptads longer than is found in all intermediatefilamentproteinsfromepithelial cells of the known vertebrate cytoplasmic intermediate filaments, in particular the vertebrate neurofilaments These distinct structural properties suggest that the vertebrate and invertebrate low molecular weight neurofilaments evolved independently fromprimordial intermediate filament proteins. 1st and 4thresidues of the heptad areusually hydrophobic or reactivities; whereas the same non-neuronal intermediatfeilnonpolar These rod domains contain the same numa-ment proteins can be found in a variety of invertebrate cell ber and distributionof heptad repeats, theirindividual amino types [6, 7]. M64 717 and M64 718. $ Current address: Dept. of Biological Sciences, University at Albany, State University of New York, Albany, NY 12222
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