Standard Intein Gene Expression Ramps (SIGER) for protein-independent expression control

Coordination of multi-gene expression is one of the key challenges of metabolic engineering for the development of cell factories. Constraints on translation initiation and early ribosome kinetics of mRNA are imposed by features of the 5UTR in combination with the start of the gene, referred to as the "gene ramp", such as rare codons and mRNA secondary structures. These features strongly influence translation yield and protein quality by regulating ribosome distribution on mRNA strands. The utilization of genetic expression sequences, such as promoters and 5UTRs in combination with different target genes leads to a wide variety of gene ramp compositions with irregular translation rates leading to unpredictable levels of protein yield and quality. Here, we present the Standard Intein Gene Expression Ramps (SIGER) system for controlling protein expression. The SIGER system makes use of inteins to decouple the translation initiation features from the gene of a target protein. We generated sequence-specific gene expression sequences for two inteins (DnaB and DnaX) that display defined levels of protein expression. Additionally, we used inteins that possess the ability to release the C-terminal fusion protein in vivo to avoid impairment of protein functionality by the fused intein. Overall, our results show that SIGER systems are unique tools to mitigate the undesirable effects of gene ramp variation and to control the relative ratios of enzymes involved in molecular pathways. As a proof of concept of the potential of the system, we also used a SIGER system to express two difficult-to-produce proteins, GumM and CBM73. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=112 SRC="FIGDIR/small/471673v2_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@1c759acorg.highwire.dtl.DTLVardef@d03c87org.highwire.dtl.DTLVardef@135d6f9org.highwire.dtl.DTLVardef@1b48eac_HPS_FORMAT_FIGEXP M_FIG C_FIG