Silent gene clusters

Another possibihty to gain the product encoded by a silent gene cluster can be achieved by a method called the in vitro reconstitution approach. A necessity is that the substrates of the pathway are predictable. The in vitro reconstitution of an entire biosynthetic pathway usually involves the separate overexpression of each gene, the purification of the resulting protein and the performance of enzymatic studies. Thus, the discovery of a fully elaborated metabolic product by this approach is likely to be very laborious. For example, after discovering a cryptic sesquiterpene synthase in the genome of S. coelicolor (64), the new epi-isozaene (8) could be produced successfully. This metabolite was shown to be an intermediate in the assembly line of the known Streptomyces sesquiterpene albaflavenone (9) (135). 

A further possibility in revealing products of silent gene clusters is the expression of putative pathway-specific activator genes upstream or within the putative cryptic biosynthetic gene clusters. This approach is based on the incorporation of an... 

Fungal secondary metabolites — strategies to activate silent gene clusters. Fungal Genet. Biol, 48 (1), 15-22. 

Using transcriptional analyses, several cryptic biosynthetic gene clusters have been found to be silent (not expressed) under a variety of growth conditions. Such clusters may represent a rich source of new metabolites, which cannot he accessed unless expression of the genes can be activated. Several approaches have been developed to overcome the problem of silent cryptic biosynthetic gene clusters. 

The completion of the sequence of the two Streptomyces genomes demonstrated that between 5 and 6.6% of the whole genome are directly involved in the biosynthesis of predominantly unknown secondary metabolites (see above). Prior to genome sequencing, a number of reports were published in which cryptic or silent secondary metabolite pathways were identified during the search for gene clusters for known metaboKtes. Hence, the occurrence of... 

Yamanaka, K., Reynolds, K.A., Kersten, R.D., Ryan, K.S. et al (2014) Direct cloning and refactoring of a silent lipopeptide biosynthetic gene cluster yields the antibiotic taromycin A. Proc. Natl. Acad. Set U.S.A., 111 (5), 1957-1962. 

Activating the Potential of Silent Biosynthetic Gene Clusters... 

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