Certain une mutants in the nematode Caenorhabditis elegans, such as unc-14 and unc-51, show abnormal axonal elongation and axonal structures. We cloned the unc-51 gene previously and predicted that it encodes a novel serine/threonine protein kinase. In this study, we precisely localized the activity to rescue an unc-14 mutation. Also, we identified four cDNA clones encoded by the unc-14 rescuing region, in screens for proteins that bind to UNC-51 using a yeast two-hybrid system. A mutation site in the cDNA was identified for each of the six unc-14 mutants, establishing that the unc-14 gene was cloned. The unc-14 gene encodes a novel protein of 665 amino acids, and is coexpressed with the unc-51 gene in the cell bodies and axons of almost all neurons including DD/VD and hermaphrodite-specific neurons. Another clone recovered in the two-hybrid screen encodes a carboxy-terminal region of UNC-51. Analysis using the yeast two-hybrid system suggested that a central region of UNC-14 bound to a carboxy-terminal region of UNC-51, and that the UNC-51 carboxy-terminal region oligomerized. In in vitro binding studies using recombinant fusion proteins, UNC-14 interacted with UNC-51 directly. We propose that UNC-51 protein kinase acts as an oligomer, and that UNC-14 is a regulator of UNC-51, in axonal elongation and guidance.
