coli were prepared according to the method of Hanahan [39]. Exponentially growing cells (OD595 of about 6.0) were harvested for RNA preparation. Total RNA was isolated using Trizol reagent (Invitrogen, USA) according to the manufacturer’s instructions. RNA was resuspended in diethylpyrocarbonate (DEPC)-treated

water. The concentration of RNA was determined by OD260 absorption, and RNA was analyzed by electrophoresis on 1.5% formaldehyde-morpholinepropanesulfonic-agarose gel. Reverse transcription-PCR (RT-PCR) was carried out with AMV Reverse learn more Transcriptase (Promega Inc., Taiwan) according to manufacturer’s instructions. RNA (1 μg) was subjected to RT-PCR containing click here CaroS2_re_1 used as a reverse primer in first-strand cDNA synthesis. The RT mixtures were diluted and used as templates in a PCR reaction with two primers CaroS2_re_1 and CaroS2_for_1 (Additional file 1, Table S1). A 2621-bp BamHI-HindIII digested selleckchem DNA fragment, including the caroS2K and caroS2I genes, was amplified from pMS2KI with primers of CarocinS2K_for2 and CarocinS2I_rev2 (Additional file 1, Table S1) and

subcloned into pET32a to give the plasmid pEN2K (Additional file 1, Figure S5). The pES2KI was obtained by excision of the Tag element between the rbs (ribosome binding site) and start code (for CaroS2K) in pEN2K using the SLIM method as previously described [40, 41]. The 5IHT32a2KI_forT, 5IHTGT2KI_forS, 5IHT32a3KI_revT, and 5IHT32a4KI_revS primers were used. A 273-bp fragment of the caroS2I gene was amplified by PCR and ligated into the NdeI and XhoI site of pET30b to form the plasmid pEC2I. Similarly, the plasmid pES2I was obtained by deleting the (His)6-tag of pEC2I (carried out as described above with primers of X21_forT, X21_forS, X21_revT and X21_revS). Subsequently, Urease pES2KI and pES2I were introduced into E. coli BL21 (DE3) cells, respectively. Restriction DNA library screening and Southern blots Southern blots were performed according to the DIG Application Manual (Roche, USA). A 543-bp

DNA fragment (TF1-2 probe) was amplified with TF1-2P and TF1-2A2 primers (Additional file 1, Table S1), subcloned into pGEM-T Easy vector (Promega Inc., USA), and labeled using a Random Primed DNA Labeling Kit (Roche Diagnostics, USA). The genomic DNA of the wild-type strain F-rif-18 was digested with various restriction endonucleases, with sites located outside the putative open reading frame. Samples were electrophoresed and analyzed with Southern blotting. After detection using the TF1-2 probe, the DNA from positive gel slices was purified and cloned into pMCL210 to give the carocin-producing plasmid pMS2KI. The pMS2KI construct was isolated and detected as above with the TF1-2 probe. Protein purification The transformant cells of BL21, harboring pES2KI or pES2I, were grown in 500 ml to an OD595 of 0.4. The cells were induced with isopropyl-β-D-thiogalactopyranoside (IPTG; final concentration, 0.1 mM; at 25°C for 12 h).