Byk et al. (1996) isolated and characterized a novel mouse phosphoprotein with significant homology to Unc33, a protein important for neuritic outgrowth and guidance in C. elegans. The cDNA isolated from mouse brain has an open reading frame that encodes a protein of 570 amino acids with a predicted molecular mass of 61,940 Da and a theoretical pI of 6.3. This sequence shows consensus sites for several protein kinases, corroborating biochemical studies indicating the phosphorylation of partially purified ULIP with protein kinase A (PKA), casein kinase-2 , and CDC2 kinase . ULIP was found to be cytoplasmic in PC12 cells, and it exclusively associated with neurons, particularly at neuromuscular junctions. Byk et al. (1996) stated that 3 human ESTs show between 76 and 96% overall identity to the mouse ULIP sequence.