Non-catalytic subunit of the NatB complex which catalyzes acetylation of the N-terminal methionine residues of proteins beginning with Met-Asp or Met-Glu (By similarity). Required for chromosome organization and arrangement; specifically for assembly of the central region components of the synaptonemal complex onto chromosomes during meiosis and for DNA double stranded break formation and repair (PubMed:18535664, PubMed:25768301). Acts downstream of xnd-1 to regulate levels of histone acetylation in germ and somatic cell nuclei by controlling acetyl-CoA production through antagonizing the acetyl-CoA hydrolase activity of acer-1 (PubMed:25768301). Component of the N-terminal acetyltransferase B (NatB) complex (By similarity). Interacts with acer-1 (PubMed:25768301). Localizes to meiotic germline nuclei where it is first expressed in early prophase nuclei with expression increasing as nuclei progress into the pachytene stage. Expressed from interphase to prophase and at low levels from prometaphase to anaphase in mitotic nuclei. Highly expressed on autosomes during early to mid prophase. Expressed in germline and somatic cells. Expressed in embryo and adult. High embryonic and larval lethality with viable progeny displaying a high incidence of males phenotype (PubMed:18535664, PubMed:25768301). Defective chromosomal morphogenesis, segregation and alignment due to the failure of central region components of the synaptonemal complex to assemble onto chromosomes during meiosis (PubMed:18535664). Severe chromosomal and meiotic defects include a delay in chromosome dispersal upon entry into the pachytene stage; impaired stability of homologous pairing interactions resulting in a failure to form chiasmata for crossover recombination, and increased DNA double strand break repair upon entry into and throughout the pachytene stage of meiosis possibly resulting in impaired meiotic recombination (PubMed:18535664). Germ cell defects resulting in increased germ cell apoptosis (PubMed:18535664). Decreased histone acetylation in meiotic germ cell nuclei from the premeiotic tip to the late pachytene stage with the most prominent decrease upon meiotic entry and during the pachytene stages (PubMed:25768301). Decreased acetyl-CoA production (PubMed:25768301). RNAi-mediated knockdown results in reduced histone H2AK5 acetylation (PubMed:25768301). Belongs to the MDM20/NAA25 family.