The differences between secretion and DNA import also creates new demands for the ComB system. The first step in natural transformation is the binding of the extracellular double-stranded DNA. Next, transforming species usually restrict the DNA into fragments of a suitable length before transport into the cytoplasm. The imported DNA is normally single stranded (ss) [2]. Vir and other type IV secretion systems involved in conjugation also transfer ss DNA. Therefore, at least a DNA-binding function and probably also endonuclease and ss DNA-degrading functions are required in the comB system. It is tempting to speculate these tasks are fulfilled by one or more proteins that interact with ComB7, in analogy to the T-pilus association with VirB7 in A. tumefaciens [21]. A candidate protein for DNA binding or processing is ComH, a putatively exported protein necessary for DNA translocation in H. pylori, with homologs neither in other naturally transformable bacteria nor in type IV secretion systems [22. L.C. Smeets et al., comH, a novel gene essential for natural transformation of Helicobacter pylori. J. Bacteriol. 182 (2000), pp. 3948–3954. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (35)22]. With the analogy to type IV secretion systems in mind, an outline of a minimal H. pylori DNA-uptake system is shown in Fig. 2. ComB-like transformation in other species Usually, being the first of a kind means being the only one for a limited time. In the case of the comB transformation system, the runner-up is located on the Campylobacter jejuni plasmid pVir. The partial sequence of this plasmid revealed a locus with the same organization as the H. pylori comB8, comB9 and comB10 genes, with not, vert, similar55% sequence similarity [23]. Bacon et al. showed that a null mutant in the comB10 homolog attenuated adherence to and invasion of INT407 cells of the host strain, but also reduced its transformation competence by 80% and the authors concluded that this operon is also involved in natural transformation. Thus, pVir appears to contain the first described plasmid-encoded transformation system. Mutants in this plasmid-borne comB system still have significant transformation activity. In addition, some plasmid-less C. jejuni strains such as NCTC11168 are highly competent for transformation. An alternative DNA-uptake system must therefore be present in C. jejuni, although the chromosomal sequence of C. jejuni NCTC11168 does not contain homologs of comB8, comB9 and comB10 [24]. As plasmids are more prone to transfer between bacterial species, the plasmid-encoded comB homologs implicated in transformation of C. jejuni by Bacon et al. might also be present in other bacteria, and thus could serve in natural transformation of a wide range of bacterial species. *** Campylobacter jejuni plasmid pVir **** ============================== Natural transformation competence in Helicobacter pylori is mediated by the basic components of a type IV secretion system.pdf ComB8, ComB9, ComB10 are absolutely essential to natural transformation ComB7 is not essential, but stabilizes the apparatus and modulates transformation efficiency hp0333 was also shown to be necessary for transformation novel competence gene: ComH hp0039/40 -> comB9 hp0041/42 -> comB10 "The complete genome sequence of Helicobacter pylori strain P12." Fischer W., Windhager L., Karnholz A., Zeiller M., Zimmer R., Haas R. Submitted (OCT-2008) to the EMBL/GenBank/DDBJ databases Cited for: NUCLEOTIDE SEQUENCE [LARGE SCALE GENOMIC DNA]. comB10 competence protein http://www.uniprot.org/uniprot/B6JPD6 comB10 sequence: B6JPD6 comB9 sequence: B6JPD5 comB8 sequence: B6JPD4_HELP2 http://www.uniprot.org/uniprot/B6JPD4.fasta http://www.uniprot.org/uniprot/B6JPD5.fasta http://www.uniprot.org/uniprot/B6JPD6.fasta >tr|B6JPD4|B6JPD4_HELP2 ComB8 competence protein OS=Helicobacter pylori (strain P12) GN=comB8 PE=4 SV=1 MREKPFNSEQLIYLEELLSYQEKHLENKLSGFSVNDLDMQSVFRLERNRLKIAYKLLGLM SFIALILAIVLISVLPLQKTEHHFVDFLNQDKHYAIIQRADKSISSNEALARSLIGAYVL NRESINRIDDKSRYELVRLQSSSKVWQRFEDLIKTQNSIYAQSHLEREVHIVNIAIYQQD NNPIASVSIAAKLLNENKLVYEKRYKIVLSYLFDTPDFDYASMPKNPTGFKITRYSITEI APTNRND >tr|B6JPD5|B6JPD5_HELP2 ComB9 competence protein OS=Helicobacter pylori (strain P12) GN=comB9 PE=4 SV=1 MRKFLYALMGLLLAFSTLKADDFLEEANETAPAHLNHPMQDLNAIQGSFFDKNRSKMSNT LNIDYFQGQTYKIRLRYAMATLLFFSKPISDFVLGDKVGFDAKILESNDRILLIKPLQIG VDSNISVIDSEGKIFSFYVFSTTFTSSKHPNLQVFIEDKNYYSNAFLKPQKENKENVLEN ALENTPTNNKPLKEEKEEAKEKEEETIIIGDNTNAMKIVKKDIQKGYKALKSSQRKWYCL GICSKKSKLSLMPEEIFNDKQFTYFKFDKRLALSKFPVIYKVVDGYDNPVNTRIVGDYII AEDVSTKWTLRLGKDYLCIRFVKKGKDE >tr|B6JPD6|B6JPD6_HELP2 ComB10 competence protein OS=Helicobacter pylori (strain P12) GN=comB10 PE=4 SV=1 MNKWLKGAIVFVGGFATITTISLVYHQKPKAPLNNQPSLLNDDEVKYPLQDYTFTQNPQP TNTESSKDTTIKALQEQLKAALKALNSKEMNHSKEETFKSPPIEPKTNTTPPKKDFSLKQ LDLLAARITPFKQSPKNYEENLIFPMDNPKGIDGFTNLKEKDIATNENKLLRTITADKMI PAFLITPISSQIAGKVIAQVESDIFAHMGKAVLIPKGSKVIGYYSNNNKMGEYRLDIVWS RIITPHGINIMLTNAKGADIKGYNGLVGELIERNFQRYGVPLLLSTLTNGLLIGITSALN NRGNKEGVTNFFGDYLLMQLMRQSGMGINQVVNQILRDKSKIAPIVVIREGSRVFISPNT DIFFPIPRENEVIAEFLK