Molecular genetic methods for improving secondary-metabolite production in actinomycetes.

The practical applications of genetic engineering to improve secondary-metabolite production in actinomycetes are potentially numerous, but have been limited by: (1) restriction barriers, which can hinder the introduction of DNA into many actinomycetes; (2) self-replicating plasmid-cloning vectors, which generally inhibit secondary-metabolite production; and (3) recombinants containing heterologous DNA, which may be subject to additional regulatory hurdles. Recently, intergeneric conjugation has been used to circumvent host restriction, and integration of cloned DNA into neutral genomic sites prevents product inhibition by self-replicating plasmids, and has enabled construction of recombinant strains lacking heterologous DNA sequences. The rpsL system permits direct selection for gene replacements and gene insertions that can facilitate this process.