In order to identify potential NS2B3 targets we performed a bioinformatic search for potential DENV protease cleavage sites contained within members of the type I IFN pathway [32] . We identified putative cleavage sites in several known members of the type I IFN pathway (see table 1 ). After testing the factors shown in table 1 for their susceptibility to be cleaved by the DENV protease NS2B3, we observed that only STING was cleaved in our experimental set up (data not shown and figure 1). We have generated a wild type DENV-NS2B3, and a proteolytically inactive version (NS2B3-S135A), ( Figure 1A ) by direct mutagenesis [25] that were used to analyze the potential cleavage of STING by the DENV protease complex. When we compared the human amino acid sequence of human STING to its mouse counterpart we noticed that the putative NS2B3 cleavage site in hSTING which is situated at the beginning of transmembrane domain 3 ( Figure 1B ), is absent in mouse STING. In order to test the susceptibility of human and mouse STING proteins to proteolytic cleavage or degradation, we co-expressed a Cterminally HA-tagged STING alongside a wild type or catalytically active DENV-NS2B3, and a proteolytically inactive version (NS2B3-S135A) in 293T cells, ( Figure 1A ) and analyzed them by western blot (Figures 1C, 1D ). In the presence of WT NS2B3 we observed the full-length 42 kDa human STING and an additional band of about 32 KD, which is consistent with a C-terminal region product of a cleavage occurring within the first 96 aa of STING ( Figure 1C ). The additional band was not visible when the mouse version of STING or a catalytically inactive NS2B3 was used ( Figure 1C and 1D ). This putative cleavage site for the DENV NS2B3 lies very close to the conserved cysteine motif C88xxC91, or redox motif, recently described to be required for dimerization of STING and subsequent signaling in the type I IFN production pathway [33] . Regardless of their susceptibility to cleavage by the DENV NS2B3 complex, both the human and mouse versions of STING co-immunoprecipitated with the WT DENV NS2B3 complex and the proteolytically inactive mutant NS2B3 S135A ( Figure 1E , lanes 2, 3, 6 and 7). To map the putative cleavage site of human STING for the DENV NS2B3 complex, we mutated the sequence corresponding to the first three amino acids of the human site, RRG (shown in figure 1B as hSTING in red) with the sequence corresponding to the amino acids HCM found in the mouse version of STING (shown in figure 1B as mSTING). These recombinant versions of STING were co-transfected into 293T cells with the WT and mutant version of the NS2B3 protease and the ability of the DENV protease to cleave STING ( Figure 1F , lane 5) was drastically reduced when the mouse sequence was present in hSTING ( Figure 1F , lane 2). These data confirm the requirement for amino acids RRG for efficient cleavage of STING by the DENV NS2B3. However, replacement of the corresponding amino acid sequence of mouse STING (IHCM) by the human putative cleavage sequence (LRRG) does not render mouse STING susceptible to cleavage by the DENV protease ( Figure 1G , lane 2), suggesting that additional flanking amino acids are required for this cleavage. Altogether, these results strongly suggest that STING is a target for NS2B3 in human cells and possibly a restriction factor for DENV infection in the mouse.