The level of a transcript required for production of a Streptomyces coelicolor antibiotic is conditionally dependent on a tRNA gene

Abstract

In Streptomyces coelicolor A3(2), bldA mutants are conditionally defective in aerial mycelium formation and fail to synthesize all four antibiotics produced by bldA+ strains. Previous studies showed that bldA specifies the tRNA for the rarely used leucine codon UUA. Here we describe experiments examining the abundance in a bldA mutant of a transcript involved in antibiotic production. With use of a bacteriophage-based integrative vector, a promotorless xylE reporter gene was inserted into a previously undescribed gene for an early step in biosynthesis of the red antibiotic undecylprodigiosin, located in the red gene cluster. With this transcriptional fusion present at unit copy number in the chromosome, xylE expression in a bldA+ strain was maximal late in growth in a liquid production medium and was virtually absent in a bldA mutant. On plates of a different medium, the bldA mutant was able to produce undecylprodigiosin and to express the red::xylE fusion, but both abilities were repressed by increasing the concentration of phosphate in the medium. These experiments showed that the undecylprodigiosin deficiency of bldA mutants cannot be accounted for by the presence of TTA codons in the red structural genes, but rather that bldA influences red gene mRNA abundance. In low-phosphate conditions, an alternative regulatory pathway can lead to red gene expression.

TTA codons in some genes prevent their expression in a class of developmental, antibiotic-negative, Streptomyces mutants.

“…3) or on the rich medium R2YE. The same result was seen on MM plus mannitol with low phosphate (0.04 mM), conditions in which one of the S. coelicolor antibiotic pathways (for undecylprodigiosin synthesis) is expressed in the bldA39 mutant J1700 (30 (Fig. 4, was used to transform J1725 (S. lividans, bldA39).…”

Regulation of Aspergillus nidulans penicillin biosynthesis and penicillin biosynthesis genes acvA and ipnA by glucose

“…The growth phase is called the trophophase, whereas the secondary metabolite production phase is termed the idiophase (reviewed in reference 29). A strict separation of both phases, with production of secondary metabolites virtually only in the idiophase, has been observed in antibiotic-producing bacterial cultures (19,27). By comparing regulatory circuits of several antibiotic biosyntheses, Martin and Demain (29) concluded that the separation between trophophase and idiophase is not so clearcut in filamentous fungi.…”

The use of a rare codon specifically during development?

“…In contrast, there is no TTA codon in redD (Narva and Feiteison, 1990). To explain the btdAdependence of the red structurai genes, Guthrie and Chater (1990) proposed that a second pathway-specific regulatory gene for the red genes which does contain a TTA codon is also necessary for their activation. Why should there be differences in the role of bidA between pathways?…”

“…for the actinorhodin and undecylprodigiosin pathways, respectively, show evidence of homology throughout, and they are therefore likely to have a simitar mode of action (FernandezMoreno etai, 1991: Narva andFeitelson, 1990). Representative structural act genes controlled by acfll-ORF4 and red genes controiled by redD are transcriptionally virtually silent in a btdA mutant {Guthrie and Chater, 1990;Bruton et ai. 1991).…”