KINESIN MESSENGER-RNA IS PRESENT IN THE SQUID GIANT-AXON

Recently, we reported the construction of a cDNA library encoding a he terogeneous population of polyadenylated mRNAs present in the squid gi ant axon. The nucleic acid sequencing of several randomly selected clo nes led to the identification of cDNAs encoding beta-actin and beta-tu bulin, two relatively abundant axonal mRNA species. To continue charac terization of this unique mRNA population, the axonal cDNA library was screened with a cDNA probe encoding the carboxy terminus of the squid kinesin heavy chain. The sequencing of several positive clones unambi guously identified axonal kinesin cDNA clones. The axonal localization of kinesin mRNA was subsequently verified by in situ hybridization hi stochemistry. In addition, the presence of kinesin RNA sequences in th e axoplasmic polyribosome fraction was demonstrated using PCR methodol ogy. In contrast to these findings, mRNA encoding the squid sodium cha nnel was not detected in axoplasmic RNA, although these sequences were relatively abundant in the giant fiber lobe. Taken together, these fi ndings demonstrate that kinesin mRNA is a component of a select group of mRNAs present in the squid giant axon, and suggest that kinesin may be synthesized locally in this model invertebrate motor neuron.