RAX or PRKRA (retina and anterior neural fold homeobox) is a homeobox-containing transcription factor. It plays an important role in eye development by regulating the initial specification of retinal cells. In the absence of double-stranded RNA, RAX activates EIF2AK2/PKR, so as to phosphorylate EIF2S1/EFI2-alpha leading to inhibition of translation and induction of apoptosis. RAX has been reported to be essential for siRNA production by DICER1 and for subsequent siRNA-mediated post-transcriptional gene silencing. Mutations in this gene have been reported in patients with defects in ocular development, including microphthalmia, anophthalmia and coloboma. RAX is expressed in blood, bone, brain, spleen and adipose tissues.