Proper nucleosome assembly is critical for compacting DNA into chromatin. In human and mouse there are 5 protein-coding genes which comprise the nucleosome assembly protein (NAP) family. NAP1L1 (NAP1) and NAP1L4 (NAP2) are ubiquitously expressed family members which have been the most extensively studied. The remaining three family members, NAP1L2, NAP1L3 and NAP1L5 are neuron-specific nucleosome assembly proteins translated from intronless genes which are monoallelically expressed. NAP1L2 (nucleosome assembly protein 1-like 2), also known as BPX (brain specific protein, X-linked), is a 460 amino acid protein containing acidic domains which are thought to mediate histone interactions. NAP1L2 binds to chromatin and interacts with Histones H3 and H4. The function of NAP1L2 is not clearly defined although evidence suggests that NAP1L2 influences histone acetylation and therefore may play a significant role in regulating transcription in developing neurons.