Notably, the Lys 92 deletion mutant results in a decreased deubiquitinating enzyme activity of 27.04% compared to wild type. We also determined the relative expression levels of Usp46 in rat tissues using real-time RT-PCR. Usp46 mRNA was expressed in various tissues examined including brain, with the highest expression in spleen. In addition, like rat USP46, both human and mouse USP46 are active toward to the model substrate, suggesting that the USP cleavage assay using GSTUb52 as a model substrate is simple for testing the deubiquitinating enzyme activity of USP46. These results peptides sh2 indicate that the Lys92 deletion of USP46 could influence deubiquitinating enzyme activity and therefore might contribute to the understanding of neural and genetic mechanisms that underlies the mental disorders associated with USP46. In the present study, we report that USP46 has deubiquitinating enzyme activity detected by USP cleavage assay using GST-Ub52 as a model substrate. We find that, compared to wild type, the Lys 92 deletion mutant results in a decreased enzyme activity of 27.04%. This work indicates that behavioral despair associated mutant of the Lys 92 deletion of USP46 could influence enzyme activity and therefore might contribute to the understanding of the molecular mechanisms of the mental disorders associated with USP46. In addition, we also determined the relative expression levels of Usp46 in rat tissues using real-time RT-PCR. Usp46 mRNA is expressed in various tissues examined including brain, with the highest expression in spleen. Our data reveal that USP46 has deubiquitinating enzyme activity detected by USP cleavage assay using GST-Ub52 as a model substrate. Our findings are in good agreement with previous study in the enzyme activity of USP46 detected by the cleavage assay using Ub-Met-b-gal as a substrate using western bolt method. The both methods co-expressed USP and model ubiquitin fusion protein substrate in a bacteria based system, though different model substrate were used, suggesting that USP46 has deubiquitinating enzyme activity by itself toward the model substrate in bacterial cells. On the other hand, Cohn MA et al reported that both USP46 and USP12 deubiquitinating enzymes have weak activity by themselves, and that their activities are stimulated by UAF1 strongly. They conclude that the enzyme activity of both USP46 and USP12 are regulated by UAF1. In the study, they assessed the deubiquitinating activity by an in vitro deubiquitinating enzyme assay using ubiquitin-AMC as a substrate. The differences in the detection systems might account for the difference in enzyme activity of USP46 between those studies. Cohn et al hired an in vitro system using ubiquitin-AMC as a model substrate. The system is relative new, and needs purified enzyme from Sf9 insect cells, since the most USPs is insoluble when expressed in E. coli. This is also the case in USP46. In contrast, both the current study and Quesada et al used a bacterial expression system using either Ub-Met-b-gal or GST-Ub52 as model substrates. In those systems, the enzyme substrate interaction happens in bacterial cells and no protein purification is needed. In addition, like rat USP46, both human and mouse USP46 are active toward to the model substrate in our detection system, indicating the USP cleavage assay is a stable method to detect deubiquitinating enzyme activity of USP46. Usp46 with a Lys 92 deletion is closely associated with loss of ��behavioral despair�� under inescapable stresses in addition to abnormalities in circadian behavioral rhythms and the GABAergic system.