Human ribosomal proteins play important structural and functional roles in the ribosome and in protein synthesis. An efficient method to recombinantly produce and purify these proteins would enable their full characterisation. However, the production of human ribosomal proteins can be challenging. The only published method about the recombinant production of human ribosomal proteins involved the recovery of proteins from inclusion bodies, a process that is tedious and may lead to significant loss of yield. Herein, we explored the use of different Escherichia coli competent cells and fusion protein tags for the recombinant production of human ribosomal proteins. We found that, by using thioredoxin as a fusion protein, soluble ribosomal protein could be obtained directly from cell lysates, thus leading to an improved method to recombinantly produce these proteins.

In Escherichia coli the expression of heterologous genes for the production of recombinant proteins can be challenging due to the codon bias of different organisms. The rare codons AGG and AGA are amongst the rarest in E. coli. In this work, by using the human gene RioK2 as case study, we found that the presence of consecutive AGG-AGA led to a premature stop, which may be caused by an event of -1 frameshift. We found that translational problems caused by consecutive AGG-AGA are sequence dependent, in particular in sequences that contain multiple rare AGG or AGA codons elsewhere. Translational problems can be alleviated by different strategies, including codon harmonisation, codon optimisation, or by substituting the consecutive AGG-AGA codons by more frequent arginine codons. Overall, our results furthered our understanding about the relationship between consecutive rare codons and translational problems. Such information will aid the design of DNA sequence for the production of recombinant proteins.