lividans TK24. Heterologous expression of these genes resulted in the production of 2-hydroxy-7-methoxy-5-methyl-1-naphthoic this website acid, indicating the complete biosynthesis pathway of the final NA moiety in the NCS structure. Escherichia coli XL1 Blue MRF’ (Stratagene) was used for DNA amplification and preparation of recombinant plasmids (Table 1). Escherichia coli
ET 12567 was used to propagate nonmethylated DNA. Streptomyces carzinostaticus ATCC 15944 was the parent strain and was grown in R2YE liquid media for isolation of genomic DNA. Streptomyces lividans TK24 was used as the heterologous host. Protoplast transformation was carried out according to the standard protocol (Kieser et al., 2000). For the preparation of protoplasts and plasmid DNA, R2YE liquid media and R2YE agar plates were used. For product isolation, S. lividans TK24 harboring the expression plasmids were cultivated at 28 °C for 5 days in YEME media (Kieser et al., 2000). Antibiotics, ampicillin (100 μg mL−1), and GDC-0199 mw thiostrepton (50 μg mL−1) were used whenever necessary. The expression vector, pIBR25, under the control of the ermE* promoter, which leads to the transcription of DNA in Streptomyces species, was used for cloning. In our previous study, we have constructed recombinant plasmid pNBS2, harboring ncsB naphthoic acid synthase in pIBR25 (Sthapit et al., 2004) (Fig. 2). The ncsB1 was amplified by PCR of genomic
DNA from S. carzinostaticus, using two synthesized oligonucleotide primers NeO-MT-HF and NeO-MT-HR (Table 2). The PCR was conducted in a thermocycler (Takara, Japan) under the following conditions:
30 cycles of 30 s at 95 °C, 1 min at 55 °C, and 1 min at 72 °C. The PCR product was cloned into pGEM®-T Easy vector (Promega) and sent for sequencing to avoid the mutation of DNA during the cloning process. The PCR product (1 kb) was cloned into the HindIII sites of pNBS2, yielding the recombinant plasmid pNA-B1. The correct construct was identified by a restriction enzyme analysis. The ncsB3 (1.2 kb) was amplified by PCR of genomic DNA from S. carzinostaticus, using two synthesized oligonucleotide primers, P450-FX and P450-RP (Table 2). Similarly, ncsB1 (1 kb) was Molecular motor also amplified using OMT-BF and OMT-XR (Table 2). To construct recombinant pNA-B3, ncsB3 and ncsB were cloned together into pIBR25. Another recombinant pNA-B1B3 containing three genes ncsB, ncsB3, and ncsB1 was constructed as follows: the PCR products of ncsB3 and ncsB1 were subcloned into pGEM-3Zf- with BamHI/XbaI and XbaI/PstI, respectively. The two genes were cut from pGEM-3Zf- using BamHI/PstI to introduce into pIBR25. The correct construct was identified by restriction enzyme analysis. The expression vector pIBR25 and recombinants pNA-B1, pNA-B3, and pNA-B1B3 were transformed separately into S. lividans TK24 following the polyethylene glycol-mediated protoplast transformation method (Kieser et al.