Probable transcriptional regulator (PubMed:12874127, PubMed:18586090). May mediate transcriptional activation by binding to the E-box motif 5'-CANNTG-3' (PubMed:9187144, PubMed:12874127). Plays a role in the differentiation of the hermaphrodite-specific motor neurons (HSN) that are required for normal egg laying (PubMed:18586090). Might play a role in serotonin production by regulating expression of the tryptophan hydrolase tph-1 which catalyzes serotonin synthesis, in the HSN neurons (PubMed:18586090). Also plays a role in HSN axon guidance towards the vulva and the ventral nerve cord, possibly by promoting the expression of the netrin receptor unc-40 (PubMed:18586090). Under feeding conditions, involved in the regulation of the srh-234 chemoreceptor encoding gene expression in the ADL sensory neurons (PubMed:27487365). Together with hlh-2, involved in the induction of programmed cell death in the sister cells of the serotonergic neurosecretory motor (NSM) neurons, probably through the activation of egl-1 transcription (PubMed:12874127). Efficient DNA binding requires dimerization with another bHLH protein. Forms a heterodimer with hlh-2. Expressed in the ADL sensory neurons. Expressed in neuronal precursor cells during embryogenesis (PubMed:9187144, PubMed:27487365). Expressed in nerve ring ganglia neurons in very early larval stage L1, which is undetectable by early larval stage L1 (PubMed:18586090). During L1, expressed in the P cell lineage, specifically in the ectodermal-like P cells, and expression persists in the primary and secondary neural precursors of the P cell lineages (PubMed:18586090). Later, appears to be expressed in all 53 of the resulting postmitotic motor neurons during larval stage L1 (PubMed:18586090). Expression in most of these neurons is undetectable by larval stage L2 (PubMed:18586090). Also expressed in the hermaphrodite-specific motor neurons (HSN) and in the ventral type C (VC) motor neurons throughout larval development (PubMed:18586090). Expression in the HSNs persists until late L4 larval stage (PubMed:18586090). Egg-laying defective (PubMed:18586090). Reduced expression of the tryptophan hydroxylase tph-1 which leads to reduced production of the neurotransmitter serotonin in the hermaphrodite-specific motor neurons (HSN) (PubMed:18586090). Inappropriate lateral projection of HSN axons (PubMed:18586090). Lack of netrin receptor unc-40 expression in a subset of HSN and VC motor neurons (PubMed:18586090). RNAi-mediated knockdown prevents cell death of a subset of the serotonergic neurosecretory motor (NSM) neuron sister cells, and survival of NSM sister cells is increased in an hlh-2 mutant background (PubMed:12874127). Contains a degenerate basic motif not likely to bind DNA.