Exposure of mammalian cells to UV radiation was proposed to stimulate the transcription factor NF-B by a unique mechanism. Typically, rapid and strong inducers of NF-B, such as tumor necrosis factor alpha (TNF-␣) and bacterial lipopolysaccharide (LPS), lead to rapid phosphorylation and proteasomal degradation of its inhibitory protein, IB␣. In contrast, UV, a relatively slower and weaker inducer of NF-B, was suggested not to require phosphorylation of IB␣ for its targeted degradation by the proteasome. We now provide evidence to account for this peculiar degradation process of IB␣. The phospho-IB␣ generated by UV is only detectable by expressing a ⌬F-box mutant of the ubiquitin ligase ␤-TrCP, which serves as a specific substrate trap for serine 32 and 36 phosphorylated IB␣. In agreement with this finding, we also find that the IB kinase (IKK) phospho-acceptor sites on IB␣, core components of the IKK signalsome, and IKK catalytic activity are all required for UV signaling. Furthermore, deletion and point mutation analyses reveal that both the amino-terminal IKK-binding and the carboxy-terminal putative zinc finger domains of NEMO (IKK␥) are critical for UV-induced NF-B activation. Interestingly, the zinc finger domain is also required for NF-B activation by two other slow and weak inducers, camptothecin and etoposide. In contrast, the zinc finger module is largely dispensable for NF-B activation by the rapid and strong inducers LPS and TNF-␣. Thus, we suggest that the zinc finger domain of NEMO likely represents a point of convergence for signaling pathways initiated by slow and weak NF-B-activating conditions.

SummaryThe 20 common amino acids act as attractants during chemotaxis by the Gram-positive organism Bacillus subtilis. In this study, we report that all amino acids induce B. subtilis to produce methanol both upon addition and removal of the chemoeffector. Asparagine-induced methanol production is specific to the McpB receptor and aspartate-induced methanol production correlates with receptor occupancy. These findings suggest that addition and removal of all amino acids cause demethylation of specific receptors which results in methanol production. We also demonstrate that certain attractants cause greater production of methanol after multiple stimulations. CheC and CheD, while affecting the levels of receptor methylation, are not absolutely required for either methylation or demethylation. In contrast, CheY is necessary for methanol formation upon removal of attractant but not upon addition of attractant. We conclude that methanol formation due to negative stimuli indicates the existence of a unique adaptational mechanism in B. subtilis involving the response regulator, CheY.