Bose Baundauna, Auchtung Jennifer M, Lee Catherine A, Grossman Alan D
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Mol Microbiol. 2008 Nov;70(3):570-82. doi: 10.1111/j.1365-2958.2008.06414.x. Epub 2008 Aug 29.
The mobile genetic element ICEBs1 is an integrative and conjugative element (a conjugative transposon) found in the Bacillus subtilis chromosome. The SOS response and the RapI-PhrI sensory system activate ICEBs1 gene expression, excision and transfer by inactivating the ICEBs1 repressor protein ImmR. Although ImmR is similar to many characterized phage repressors, we found that, unlike these repressors, inactivation of ImmR requires an ICEBs1-encoded anti-repressor ImmA (YdcM). ImmA was needed for the degradation of ImmR in B. subtilis. Coexpression of ImmA and ImmR in Escherichia coli or co-incubation of purified ImmA and ImmR resulted in site-specific cleavage of ImmR. Homologues of immR and immA are found in many mobile genetic elements. We found that the ImmA homologue encoded by B. subtilis phage phi105 is required for inactivation of the phi105 repressor (an ImmR homologue). ImmA-dependent proteolysis of ImmR repressors may be a conserved mechanism for regulating horizontal gene transfer.
移动遗传元件ICEBs1是一种存在于枯草芽孢杆菌染色体中的整合性接合元件（一种接合转座子）。SOS反应和RapI-PhrI传感系统通过使ICEBs1阻遏蛋白ImmR失活来激活ICEBs1基因的表达、切除和转移。尽管ImmR与许多已鉴定的噬菌体阻遏蛋白相似，但我们发现，与这些阻遏蛋白不同，ImmR的失活需要ICEBs1编码的抗阻遏蛋白ImmA（YdcM）。ImmA是枯草芽孢杆菌中ImmR降解所必需的。在大肠杆菌中共表达ImmA和ImmR或纯化的ImmA和ImmR共同孵育会导致ImmR的位点特异性切割。在许多移动遗传元件中都发现了immR和immA的同源物。我们发现枯草芽孢杆菌噬菌体phi105编码的ImmA同源物是phi105阻遏蛋白（一种ImmR同源物）失活所必需的。ImmA依赖的ImmR阻遏蛋白蛋白水解作用可能是调节水平基因转移的一种保守机制。
