, 2007). However, our microarray hybridization analysis revealed that the mRNA level of the prtA in the mipXcc mutant NK2699 is similar to that in the wild-type strain 8004 (NK2699/8004 = 0.89) (data not shown). This was confirmed by semi-quantitative RT-PCR (Fig. 1a). We also constructed strain mip/pR3PrtA, in which a constitutively expressed prtA was found unable to restore extracellular TSA HDAC price protease activity. It was, however, able to restore activity in 001F10/pR3PrtA (Fig. 1b). The second possibility suggested in our previous article was that MipXcc may be required for the secretion of extracellular proteases (Zang

et al., 2007). Other studies have shown that Xcc’s extracellular enzymes are secreted via the type II secretion system (T2SS) (Hu et al., 1992; Lee et al., 2004). They acquire their native conformations in the periplasmic space before crossing the outer membrane. As shown in Fig. 2a, mature proteases accumulated in the periplasm of the T2SS-deficient mutant strain 258D12. In contrast, no mature

protease was accumulated in the periplasm of the mipXcc mutant. In addition, the prtA mutant did not display any significant protease activity after it was treated with chloroform (Fig. 2a). This indicates that proteases other than PrtA contribute little to the proteolytic activity of Xcc strain 8004. In addition, the portraits of wild-type 8004 and NK2699/pR3MipH6 suggest that not all active protease proteins are secreted BTK inhibitor cost immediately after maturation. Our previous observation that PPIase activity was much less intense in the periplasm of the mipXcc mutant strain than in the wild type suggested that MipXcc might be located in the periplasm of Xcc cells (Zang et al., 2007). In this study, we constructed a complementary strain, NK2699/pR3MipH6, which expressed MipXcc with a 6xHis tag on its C-terminus Methane monooxygenase (MipH6). As shown in Fig. 2a, the addition of the 6xHis tag to the C-terminus of MipXcc did not affect its function. We prepared the total, periplasmic,

outer membrane and extracellular protein fractions of NK2699/pR3MipH6 during the late log phase. Western blot analysis revealed MipH6 in the total-protein and periplasmic protein fractions but not in the outer membrane or extracellular protein fractions (Fig. 2b). In a parallel experiment, the Zur protein, a transcriptional regulator localized in the cytoplasm of Xcc cells (Huang et al., 2008), was detected only in the total protein fraction but not in the periplasmic and extracellular fractions (Fig. 2b). These results indicate that no cytoplasmic protein was released into the periplasmic or extracellular space. They also demonstrate that MipXcc is located in the periplasm. To determine whether or not MipXcc interacts with PrtA directly, we constructed pTRGMip and pBTPrtA without leader peptides and co-introduced them into BTHrst to create the strain BTHrst/(pBTPrtA-pTRGMip).