Southern blot technology showed that Tn5 had been inserted (Additional file 1,
Figure S1). Identification of Tn5-inserted DNA Structures To identify Tn5-interrupted genes, genomic DNA from TF1-2 was amplified with TAIL-PCR using an array of specific primers (Additional file 1, Figure S8). A 2621-bp DNA fragment, including two open reading frames (ORFs), was identified as the sequence containing the bacteriocin structural gene. This C188-9 cell line gene was designated the carocin S2 gene. To characterize the carocin S2 gene, the TF1-2 probe was designed to hybridize in Southern blots with a Bam HI-digested DNA fragment from the genomic library of F-rif-18 (Figure 2A). A 5706-bp Bam HI-digested DNA fragment (Figure 2B), harboring two complete ORFs of carocin S2, was cloned into the plasmid pMCL210 (Additional file 1, Figure S2). The carocin-producing plasmid was designated as pMS2KI. The amplicon, comprising the predicted ORF2 of caroS2I, was subcloned into the pGEM-T easy vector, resulting in the plasmid pGS2I (Additional file 1, Figure S5). Figure 2 DNA library screening and scheme of carocin S2 gene. (A) The TF1-2 probe was used to screen DNA fragments from the genomic DNA library of F-rif-18. The DNA was digested
with various restriction enzymes as follows: 1. Hpy188I; 2. HindIII; 3 HpaI; 4. EcoRV; 5. EcoRI; 6. ClaI; 7. BsaAI; 8. BglII; 9. BamHI; 10. AhdI; M. DNA leader marker; C. The TF1-2 probe DNA. The arrowhead indicates the 5.7-kb carocin S2 fragment. (B) Shown is the 5.7-kb segment of DNA containing the carocin S2. The location of TF1-2 probe and part amplicon of cDNA of caroS2K and caroS2I were shown. Transcriptional check details analysis and KU55933 cost in vivo expression of carocin S2 gene To determine whether the carocin S2 gene is transcribed in a series of recombinant strains, reverse transcription-PCR was used to estimate RNA level. Two sets of intergenic primers were designed to amplify parts of transcripts from caroS2K or caroS2I, respectively (Figure 2B). Amplification
of parts of 16S ribosomal RNA transcripts indicated that pheromone RNA in these bacterial cells is expressed at normal levels (Figure 3). Figure 3 Reverse Transcription PCR of RNA. Shown are cDNA from the following strains: Lanes 1, F-rif-18; 2, TF1-2; 3, TF1-2/pMS2KI, 4, DH5α; 5, DH5α/pMS2KI.; 6, SP33; 7, SP33/pGS2I. The amplicons of caroS2K and caroS2I are 925 bp and 259 bp, respectively. The corresponding amplicons of 16S rRNA from the examined strains (lower panel). All samples were loaded equally. The presence of the 925-bp amplicon revealed that caroS2K was being transcribed in the cell (panel caroS2K in Figure 3). The TF1-2 strain, which is a Tn5 insertional mutant, could not transcribe caroS2K (lane 2), but the ability of TF1-2 to transcribe caroS2K was restored by introduction of pMS2KI (lane 3). It was apparent that the amount of caroS2K expression was dependent on the number of copies of plasmid pMS2KI (compare lane 1 to lane 3).