Tandem repeats in precursor protein stabilize transcript levels and production levels of the fungal ribosomally synthesized and post-translationally modified peptide ustiloxin B.

Ustiloxin B is a ribosomally synthesized and post-translationally modified peptide (RiPP) first reported in Ascomycetes. Its biosynthetic pathway was recently identified in the filamentous fungus Aspergillus flavus. The precursor protein of ustiloxin B, UstA, has a signal peptide to the endoplasmic reticulum at its N-terminal and a subsequent tandemly highly repeated segment cleaved at Lys-Arg dipeptides by Kex2 protease; such proteins are called Kex2-processed repeat proteins (KEPs).

Promoter tools for further development of as a platform for fungal secondary metabolite production.

Background: The filamentous fungus is widely used for secondary metabolite production by heterologous expression; thus, a wide variety of promoter tools is necessary to broaden the application of this species. Here we built a procedure to survey genes constitutively highly expressed in 83 transcriptome datasets obtained under various conditions affecting secondary metabolite production, to find promoters useful for heterologous expression of genes in .

Results: To test the ability of the promoters of the top 6 genes to induce production of a fungal secondary metabolite, ustiloxin B, we inserted the promoters before the start codon of , which encodes the transcription factor of the gene cluster responsible for ustiloxin B biosynthesis, in .