CHARACTERIZATION OF SQUID ENOLASE MESSENGER-RNA - SEQUENCE-ANALYSIS, TISSUE DISTRIBUTION, AND AXONAL LOCALIZATION

Enolase is a glycolytic enzyme whose;amino acid sequence is highly con served across a wide range of animal species. In mammals, enolase is k nown to be a dimeric protein composed of distinct but closely related subunits: alpha (non-neuronal), beta (muscle-specific), and gamma (neu ron-specific). However, little information is available on the primary sequence of enolase in invertebrates. Here we report the isolation of two overlapping cDNA clones and the putative primary structure of the enzyme from the squid (Loligo pealii) nervous system. The composite s equence of those cDNA clones is 1575 bp and contains the entire coding region (1302 bp), as well as 66 and 207 bp of 5' and 3' untranslated sequence, respectively. Cross-species comparison of enolase primary st ructure reveals that squid enolase shares over 70% sequence identity t o vertebrate forms of the enzyme. The greatest degree of sequence simi larity was manifest to the a isoform of the human homologue. Results o f Northern analysis revealed a single 1.6 kb mRNA species, the relativ e abundance of which differs approximately 10-fold between various tis sues. Interestingly, evidence derived from in situ hybridization and p olymerase chain reaction experiments indicate that the mRNA encoding e nolase is present in the squid giant axon.