The only known function of CIITA is as a transcriptional coactivator; therefore, we thought it likely that it drives the expression of a gene which enhances viral protease-mediated Gag processing. Therefore, we reasoned that expression of CIITA mutants which fail to localize to the nucleus should not mediate increased Gag processing or enhanced infectious virus release. To test this idea, a panel of CIITA mutants (GTP2, a magnesium ion coordination site mutant and GTP3, a guanine ring-binding domain mutant and L1035P, a point mutant in the C-terminal leucine rich repeat domain, which are all defective for nuclear localization and fail to activate HLA-DRA transcription [56, 57, 58] ), were individually co-expressed with HIV-1 NL4-3 DNA, and infectious virus release and Gag processing were monitored. Interestingly, producer cells expressing these mutants also produced more infectious virus as compared to vector-only control ( Figure 7A ) and had increased Gag processing in both cell-bound virions and cell-free virions ( Figure 7B and Figure S4 , respectively). Loss of CIITA nuclear localization (and therefore coactivation potential), did not hinder increased Gag processing and infectious virus release, strongly suggesting that CIITA acts cytoplasmically to increase HIV virus maturation independent of its transactivation function. We further evaluated CIITA transactivation potential as a mechanism of enhanced virus release utilizing a different model system. NIH 3T3 BALB/c cells (expressing human p32 to allow for virus like particle production [59] ) expressing CIITA and transfected with an LTR-deficient HIV genome construct (pcHIV PAL),under control of a CMV promoter had a dramatic increase in virus-like particle production as compared to NIH 3T3 cells in the absence of CIITA ( Figure S5 ). This result provides further evidence that CIITA enhancement of virus production is independent of its transactivation potential on the HIV LTR.