Mouse ULK2, a novel member of the UNC-51-like protein kinases: unique features of functional domains.

The UNC-51 serine/threonine kinase of C. elegans plays an essential role in axonal elongation, and unc-51 mutants exhibit uncoordinated movements. We have previously identified mouse and human cDNAs encoding UNC-51-like kinase (ULK1). Here we report the identification and characterization of the second murine member of this kinase family, ULK2. Mouse ULK2 cDNA encodes a putative polypeptide of 1033 aa which has an overall 52% and 33% amino acid identity to ULK1 and UNC-51, respectively. ULKs and UNC-51 share a typical domain structure of an amino-terminal kinase domain, a central proline/serine rich (PS) domain, and a carboxy-terminal (C) domain. Northern blot analysis showed that ULK2 mRNA is widely expressed in adult tissues. In situ hybridization analysis indicated that ULK2 mRNA is ubiquitously localized in premature as well as mature neurons in developing nervous system. ULK2 gene was mapped to mouse chromosome 11B1.3 and rat chromosome 10q23 by FISH. HA-tagged ULK2 expressed in COS7 cells had an apparent molecular size of approximately 150 kDa and was autophosphorylated in vitro. Truncation mutants suggested that the autophosphorylation occurs in the PS domain. Although expression of ULK2 failed to rescue unc-51 mutant of C. elegans, a series of ULK2/UNC-51 chimeric kinases revealed that function of the kinase and PS domains are conserved among species, while the C domain acts in a species-specific manner. These results suggest that ULK2 is involved in a previously uncharacterized signaling pathway in mammalian cells.