IMMUNOLOGICAL PROPERTIES AND CDNA SEQUENCE-ANALYSIS OF AN INTERMEDIATE-FILAMENT-LIKE PROTEIN FROM SQUID NEURONAL TISSUE

A cDNA library has been constructed in the expression vector lambda gt 11 from mRNA isolated from squid (Loligo forbesi) optic lobes. The lib rary was screened with antibodies generated against purified squid neu rofilaments. A positive clone was isolated, which harboured a lambda g t11 recombinant having an insert size of 3.5 kb. Hybridization analysi s by Southern and northern blotting showed that the corresponding prot ein is encoded by a single gene that gives rise to a transcript of 2.6 kb. Translation of the full nucleotide sequence of the gene revealed an open reading frame covering 557 amino acids. This squid-neurofilame nt-like protein, SNLK, bears the characteristic N-terminal head, rod a nd C-terminal tail domains present in all intermediate filament (IF) p roteins. The rod has the classical heptad repeats indicating coiled-co il-forming ability, and the predicted lengths of the coils are similar to coils 1a, 1b and 2 of intermediate filaments. At the C-terminal en d of the rod there is a strongly conserved IF epitope, and a fusion pr otein containing SNLK is recognised by the panspecific intermediate fi lament antibody, IFA. A polyclonal antibody raised against SNLK has be en used to show that the protein is present only in neuronal tissues a nd that it is immunologically related to neurofilaments from Myxicola but not from mammals.