Component of the lid subcomplex of the 26S proteasome, a multiprotein complex involved in the ATP-dependent degradation of ubiquitinated proteins. In the complex, RPN6 is required for proteasome assembly (By similarity). May act as linker between 19S regulatory subunit and the 20S proteasome core. Component of the lid subcomplex of the 19S proteasome regulatory particle complex (also named PA700 complex). The 26S proteasome consists of a 20S proteasome core and two 19S regulatory subunits. Interacts with alien/CSN2. Interacts with Prosalpha2 and Rpt6. Highly expressed in the female germline, more precisely in the nurse cells of maturing egg chambers. Also detected in the somatic follicle cells. Highly expressed during oogenesis and early blastoderm embryos. After the beginning of zygotic transcription, present in the elongating germband and later in the mesodermal region and the developing hindgut and posterior midgut. In late embryos, shortly before hatching, becomes restricted to the brain hemispheres, the central nervous system, the embryonic gonads and the gut. In third instar larval tissues, expressed in the larval brain and in all imaginal disks. Embryos develop and hatch normally but fail to outlive early larval stages. During the first and second instar larval stages larvae become immobile and sluggish and die without any observable defects. Lethality is probably the result of additive defects in overall cell proliferation rather than of distinct developmental disorders. Belongs to the proteasome subunit S9 family.