Characterization of a novel regulatory gene governing the expression of a polyketide synthase gene in Streptomyces ambofaciens

Abstract

A key step in the biosynthesis of macrolide antibiotics is the assembly of a large macrocyclic lactone ring by a multienzyme protein complex called the polyketide synthase. In the species Streptomyces ambofaciens, the polyketide synthase for the assembly of the 16-membered ring of the macrolide antibiotic spiramycin is encoded by the biosynthetic gene srmG. Here we show that the accumulation of transcripts from the srmG promoter is governed by the regulatory gene srmR, whose predicted product, a 65 kDa polypeptide, is not significantly similar in its deduced amino acid sequence to that of previously reported proteins in the protein databases. The srmR gene product is also required for the accumulation of transcripts from srmX, an additional gene in the vicinity of srmR, but not for the accumulation of transcripts from srmR itself. Interestingly, mutations in srmR prevent the accumulation of transcripts from the spiramycin resistance gene srmB, but this is an indirect consequence of the failure of srmR mutants to produce spiramycin, which is an inducer of its own resistance gene. The possibility that srmR is the prototype for a new class of regulatory genes governing early events in the biosynthesis of macrolide antibiotics is discussed.

Sequencing and mutagenesis of genes from the erythromycin biosynthetic gene cluster of Saccharopolyspora erythraea that are involved in L-mycarose and D-desosamine production

“…Based on the proposed function of the eryC genes described below, however, it is possible to speculate that ery CZZ encodes either the 4-keto-6-deoxyglucose isomerase (step 1) or the reductase that completes deoxygenation at C-4 (step 3) since these steps cannot be accounted for by other gene products. However, neither of these steps is thought to be required for daunosamine biosynthesis (Otten et al, 1995 (Niemi & Mantsala, 1995) (55 YO identity), and it also strongly resembles the predicted product of srmX (52 % identity) from the spiromycin biosynthetic gene cluster of Streptomyces ambofaciens (Geistlich et al, 1992). An alignment of the deduced sequences of EryCVI, RdmD and SrmX reveals a strongly conserved nonapeptide motif, LLDVACGTG, that runs from residues 42 to 50 of the three proteins.…”

Identification and characterization of phosphoenolpyruvate: fructose phosphotransferase systems in three Streptomyces species

“…They represent one of the most important groups of organisms for medical and industrial applications (Chater & Hopwood, 1989 as they produce a diversity of antibiotics (Baltz & Seno, 1988;Chater, 1990) and extracellular enzymes (Nagaso e t al., 1988;McCarthy & Williams, 1992;Strickler e t al., 1992;Vats-Mehta e t al., 1990). Differentiation and the production of secondary metabolites, including antibiotics, are regulated by interrelated, complex mechanisms (Hopwood, 1988;Hong e t al., 1991 ;Distler e t al., 1992;Geistlich et al, 1992;Ishizuka et al, 1992;Ueda e t al., 1993). Moreover, these bacteria synthesize proteins that render them resistant to the antibiotics they produce.…”

In Vivo Analysis of the Regulatory Genes in the Nystatin Biosynthetic Gene Cluster of Streptomyces noursei ATCC 11455 Reveals Their Differential Control Over Antibiotic Biosynthesis

“…At least some of these regulators must be rather special, since they control the expression of very large polyketide synthase (PKS)-encoding genes, which implies synthesis of unusually long mRNAs. The transcriptional activator SrmR encoded within the spiramycin biosynthetic gene cluster of Streptomyces ambofaciens has been shown to be required for the transcription of at least one of the PKS genes involved in assembly of the spiramycin macrolactone ring (14). The acyB2-encoded regulator of Streptomyces thermotolerans has been shown to activate the expression of the acyltransferase gene involved in biosynthesis of the macrolide antibiotic carbomycin (2).…”