DNAJA1(DnaJ homolog subfamily A member 1), also called DJA1, HSDJ, HSPF4, is a protein that in humans is encoded by the DNAJA1 gene. The deduced 397-amino acid DNAJA1 protein is 32% identical to E. coli DnaJ, with the highest identity in the N-terminal region. Among the known DNAJ homologs in S. cerevisiae, DNAJA1 is most identical to YDJ1, which may be involved in the transport of certain proteins into the mitochondria and endoplasmic reticulum. Dja1 is expressed in mouse testis and prostate by immunohistochemical analysis and Western blot analysis.Transplantation experiments with fluorescence-tagged spermatogonia into Dja1 -/- mice revealed a primary defect of Sertoli cells in maintaining spermiogenesis at steps 8 and 9.