Members of the suppressor of cytokine signaling (SOCS) family of proteins contain C-terminal regions of homology called the SOCS box, which serves to couple SOCS proteins and their binding partners with the elongin B and C complex. Serveral other families of proteins also contain SOCS boxes but differ from the SOCS proteins in the type of domain they contained upstream of the SOCS box. Four members of the ankyrin repeat and SOCS box-containing (ASB) protein family are identified and termed as ASB-1, ASB-2, ASB-3 and ASB-4. ASB-1 is expressed in multiple organs, including the hematopoietic compartment. ASB-1 knock-out mice display a diminution of spermatogenesis with less complete filling of seminiferous tubules. Asb-2 is a novel retinoic-acid (RA)-induced gene in acute promyelocytic leukemia (APL) cells and its expression induces growth-inhibition and chromatin condensation recapitulating early events critical to RA-induced differentiaiton of APL cells. ASB-2 is directly induced by all-trans retinotic acid, by the binding of RARa to the RAR binding element/RXR binding element in the Asb-2 promoter.