CAENORHABDITIS-ELEGANS UNC-51 GENE REQUIRED FOR AXONAL ELONGATION ENCODES A NOVEL SERINE THREONINE KINASE/

Mutations in the unc-51 gene of the nematode Caenorhabditis elegans re sult in various abnormalities in axonal elongation and axonal structur es. We cloned the unc-51 gene by tagging with the transposon Tc1. The wild-type unc-51 gene, which rescued the mutant phenotypes, encodes a novel serine/threonine kinase of 856 amino acids. Mutation sites were identified in the unc-51 gene of six mutants. A Lys --> Met mutation c reated in vitro in the kinase domain led to the loss of rescuing activ ity and was dominant negative, indicating that the kinase domain of Un c-51 is essential for the function. Expression of an unc-51/lacZ fusio n gene was observed in many neurons at all stages. We propose that pro tein phosphorylation by the unc-51 product is important for axonal elo ngation and possibly for axonal guidance.