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 i ntroduction of DNA into many actinomycetes; (2) self-replicating plasm id-cloning vectors, which generally inhibit secondary-metabolite produ ction; and (3) recombinants containing heterologous DNA, which may be subject to additional regulatory hurdles. Recently, intergeneric conju gation has been used to circumvent host restriction, and integration o f cloned DNA into neutral genomic sites prevents product inhibition by self-replicating plasmids, and has enabled construction of recombinan t strains lacking heterologous DNA sequences. The rpsL system permits direct selection for gene replacements and gene insertions that can fa cilitate this process.