PRIMARY STRUCTURE AND LENS-SPECIFIC EXPRESSION OF GENES FOR AN INTERMEDIATE FILAMENT PROTEIN AND A BETA-TUBULIN IN CEPHALOPODS

Intermediate filament (IF) protein and tubulin cDNAs of cephalopod eye lenses were cloned and sequenced. The rod regions of the deduced IF p roteins of the squid and octopus were more similar (68% identical) tha n were head (33% identical) and tail (40% identical) regions. The rod sequences were closer to squid neuronal IF protein (39% identical) tha n to any other known IF protein. There was only 31% identity between t he rod regions, 21-30% identity between the head regions and 23-32% id entity between the tail regions of the present IF proteins of cephalop ods and other invertebrates. The rod regions of the cephalopod IF prot eins contained the 6 heptads characteristic of nuclear lamins, consist ent with an evolutionary relationship between IF proteins and lamins. The present octopus alpha-tubulin was 93% and beta-tubulin was 87% ide ntical to the corresponding tubulins of insects and vertebrates. SDS-P AGE and peptide sequencing indicated that the order of abundance of th e cephalopod lens cytoskeletal proteins was IF proteins, actin and tub ulins. Northern blot hybridization revealed a 4 kb mRNA for the octopu s IF protein and 2.9 and 7.3 kb mRNAs for the squid IF protein; the al pha-tubulin mRNA was about 1.8 kb in the octopus and squid, and the be ta-tubulin mRNA was about 2.8 kb in the octopus. The alpha-tubulin mRN A was present in all tissues examined; by contrast, the present beta-t ubulin and IF protein mRNAs appeared specialized for lens expression.