Involved in multiple aspects of sperm assembly including acrosome attachment, shaping of the sperm head and in the early aspects of axoneme development (PubMed:25781171). Not essential for primary cilium biogenesis (PubMed:28003339). Interacts (via guanylate kinase-like domain) with RIMBP3 (via coiled-coil region) (PubMed:28003339). Interacts (via guanylate kinase-like domain) with HOOK2 (PubMed:25781171, PubMed:28003339). Interacts (via LRRCT domain) with KLC3. Interacts with HOOK1 and HOOK3 (PubMed:28003339). Localizes to the acrosome and acroplaxome in round spermatids. Localizes to the manchette during spermiogenesis. Also found in the basal body of elongating spermatids, and in primary cilia of somatic cells. Highly expressed in the testis (PubMed:25781171). During spermatid development is initially localized to a supra-nuclear region of round spermatids, and is particularly evident at the leading edge of the developing acrosome and acroplaxome. As maturation proceeded and nuclear elongation initiated, LRGUK moves distally to ultimately reside on the microtubules of the manchette. LRGUK is also evident in the sperm basal body and the sperm tail (PubMed:25781171). Detectable at low levels from birth, up-regulated at day 14 coincident with the appearance of pachytene spermatocytes, then maximal from day 18 coincident with the appearance of haploid germ cells (PubMed:25781171). Mutagenesis with N-ethyl-N-nitrosourea (ENU) lead to the discovery of the Kaos phenotype. The Kaos mutation results in the conversion of Arg-528 to a stop codon. Homozygous males are oligoasthenoteratospermic and sterile.