Major component of the transverse central element of synaptonemal complexes (SCS), formed between homologous chromosomes during meiotic prophase. Required for chromosome loading of the central element-specific SCS proteins, and for initiating synapsis between homologous chromosomes. Chromosome loading appears to require SYCP1. Required for fertility. May play a role in apoptosis of spermatogenic cells and pathogenesis of cryptorchidism. Homodimer (PubMed:25394919). Interacts with SYCE1 (PubMed:21637789, PubMed:25394919). Interacts with SYCE2 (PubMed:21637789). Interacts with proteasome subunit PSMA8; to participate in meiosis progression during spermatogenesis (PubMed:31437213). Interacts with SPO16 (PubMed:30949703). Colocalizes with SYCE1 in the central elements. Expression is restricted to spermatocytes and is absent in spermatogonia, spermatids and spermatogonia (at protein level). Expressed in adult testis and embryonic ovary. Expressed in the convoluted seminiferous tubules in spermatogonia and spermatocytes. Expression in pubertal testes is first detected at day 12 coinciding with the onset of prophase I of meiosis (at protein level). Expression in spermatocytes first detected during zygotene when synapsis is initiated and persists on synapsed regions of homologous chromosomes until diplotene. In pachytene oocytes expression is also localized to synapsed chromosomes. Up-regulated in cryptorchid testes. Mutant mice are characterized by infertility in both sexes as well as complete disruption of synapsis initiation resulting in meiotic arrest. Initiation of meiotic recombination appears normal, but its progression is severely impaired resulting in complete absence of Mlh1 foci.