DDX3X, the X homologue of AZFa gene DDX3Y, expresses a complex pattern of transcript variants only in the male germ line.

DDX3X, the functional X homologue of the major AZFa gene, DDX3Y, belongs to the highly conserved PL10-subfamily of DEAD-box RNA helicase genes which are functionally conserved from yeast to man. They are mainly involved in cell cycle control and translation initiation control of gene transcripts with long 5'UTR extensions containing complex secondary structures. Interestingly, in humans both gene copies were found to be expressed at different phases of human spermatogenesis.