Novel Type-IVC Secretion System in Streptococcus Figure 3. The phylogenetic tree. (A) The neighbor-joining (NJ) tree obtained on the basis of the housekeeping gene rpoB. The red solid circles represent GIs with virB/D clusters. (B) NJ tree obtained on the basis of a concatenated sequence of virB4, virB6, and virD4 genes in GI. doi:10.1371/journal.pone.0046390.g003 components showed that these genes mainly work in three fields: (1) transglycosylases (such as VirB1), working for degrading peptidoglycan outside the plasma membrane of bacteria, could reduce the resistance for the secretion of substrates; (2) ATPases (VirB4, VirD4 and VirB11) play essential roles in supplying the energy for substrates translocation and apparatus assembly [4]; (3) these are still some genes contributing to the assembly of the secretion channel across inner (VirB6 and VirB8) and outer membranes (VirB7, VirB9 and VirB10). In Type-IVC secretion system of Streptococcus, although only four components were identified (VirB1, VirB4, VirB6, and VirD4), they still work in same three fields (Figure 2). VirB1-like protein, with CHAP domain, could encode amidohydrolases and is responsible for punching holes through the peptidoglycan outside of the gram-positive cell membrane. VirB4 and VirD4 could supply energizes necessary for the substrate transport [4]. VirB6, the inner-membrane protein, is to compose the transport channel across the cell membrane. Since the lack of the outer membrane in PLOS ONE | www.plosone.org 5 October 2012 | Volume 7 | Issue 10 | e46390