Construction of a stepwise gene integration system by transient expression of actinophage R4 integrase in cyanobacterium Synechocystis sp. PCC 6803

Complete Genome Sequence of Streptomyces parvulus 2297, Integrating Site-Specifically with Actinophage R4

Streptomyces parvulus 2297, which is a host for site-specific recombination according to actinophage R4, is derived from the type strain ATCC 12434. Species of S. parvulus are known as producers of polypeptide antibiotic actinomycins and have been considered for industrial applications. We herein report for the first time the complete genome sequence of S. parvulus 2297.

Actinophage R4 integrase-based site-specific chromosomal integration of non-replicative closed circular DNA

The actinophage R4 integrase (Sre)-based molecular genetic engineering system was developed for the chromosomal integration of multiple genes in Escherichia coli. A cloned DNA fragment containing two attP sites, green fluorescent protein (gfp) as a first transgene, and an antibiotic resistance gene as a selection marker was self-ligated to generate non-replicative closed circular DNA (nrccDNA) for integration. nrccDNA was introduced into attB-inserted E. coli cells harboring the plasmid expressing Sre by electroporation. The expressed Sre catalyzed site-specific integration between one of the two attP sites on nrccDNA and the attB site on the E. coli chromosome. The integration frequency was affected by the chromosomal location of the target site. A second nrccDNA containing two attB sites, lacZα encoding the alpha fragment of β-galactosidase as a transgene, and another antibiotic resistance gene was integrated into the residual attP site on the gfp-integrated E. coli chromosome via one of the two attB sites according to reiterating site-specific recombination. The integrants clearly exhibited β-galactosidase activity and green fluorescence, suggesting the simultaneous expression of multiple recombinant proteins in E. coli. The results of the present study showed that a step-by-step integration procedure using nrccDNA achieved the chromosomal integration of multiple genes.