Transcription factor (PubMed:1347150, PubMed:7904971, PubMed:28056346). Involved in motor neuron fate determination and maintenance (PubMed:28056346). In concert with unc-37, represses the expression of VB-specific genes such as ceh-12, thereby preventing the adoption of VB motor neuron fate (PubMed:7904971, PubMed:9165118, PubMed:10557206, PubMed:11245684, PubMed:17289921). Regulates synaptic specificity and the pattern of synaptic input to VA motor neurons (PubMed:1347150, PubMed:7904971, PubMed:7555714). Acts as a transcriptional repressor to counteract gene activation by transcription factor unc-3 in a subset of motor neurons, probably by binding to specific promoter elements (PubMed:28056346). Has no role in axonal guidance or outgrowth (PubMed:1347150). Interacts with unc-37. Specifically expressed in all A-type motor neurons (PubMed:7555714). The A-type motor neurons class includes 24 motor neurons; 9 DA, 3 SAB motor neurons that are generated in the embryo and 12 VAs arise after hatching in the first larval stage (PubMed:7555714). Most abundant during embryonic and larval development. Worms are unable to crawl backwards because VA motor neurons are miswired with synaptic connections normally reserved for their sister cells, the VB motor neurons. Belongs to the paired homeobox family. Unc-4 subfamily.