> You take a gene from a plant, change the codons to whatever yeast uses
This isn't necessary; codon usage is very basal. The biggest challenge you might face is prokaryotic vs. eukaryotic expression, but that's due to processing of the transcript (e.g. splicing) and the nascent peptide (e.g. all kinds of stuff). Messing with codons is simply optimization.
Expression is indeed the hard part, but not because of regulation. The general strategy is to use inducible promoters: grow the yeast, add chemical, get protein/metabolite.
Because this isn't constitutive, you can get away with a lot; even high levels of expression that will kill the cell will still produce enough of the desired product that it's an effective approach. And even relative gene-product dosage isn't too bad because you can associate the different gene products with particular known promoters and enhancers, etc.
What you have to account for is the general state of the cell; is it producing enough precursors, are intermediate products toxic, do they need to be confined for modification/processing, etc. etc. Doing complicated biochemistry gets messy.
Making simple peptides, e.g. insulin, is easy, and that's why it was the first GM pharmaceutical. Making a whole biochemical processing facility in a cell is .. a bit more of a challenge.
This isn't necessary; codon usage is very basal. The biggest challenge you might face is prokaryotic vs. eukaryotic expression, but that's due to processing of the transcript (e.g. splicing) and the nascent peptide (e.g. all kinds of stuff). Messing with codons is simply optimization.
Expression is indeed the hard part, but not because of regulation. The general strategy is to use inducible promoters: grow the yeast, add chemical, get protein/metabolite.
Because this isn't constitutive, you can get away with a lot; even high levels of expression that will kill the cell will still produce enough of the desired product that it's an effective approach. And even relative gene-product dosage isn't too bad because you can associate the different gene products with particular known promoters and enhancers, etc.
What you have to account for is the general state of the cell; is it producing enough precursors, are intermediate products toxic, do they need to be confined for modification/processing, etc. etc. Doing complicated biochemistry gets messy.
Making simple peptides, e.g. insulin, is easy, and that's why it was the first GM pharmaceutical. Making a whole biochemical processing facility in a cell is .. a bit more of a challenge.