Codon optimization to the optimal codon is not all that important unless you are going for very high level production and only in certain situations. However the presence of low frequency codons can be problematic. So if you chose codons that were in the middle or upper range for both mammals and E. coli, then you should be fine.

Dear Asma Tajik

Probably if you would like to express an human protein in mammalian the original coding sequence is it preferable than an E.coli optimized one, since codon usage is quite different .

However it really depends from the sequence of the specific gene.

Yuo can try to compare both sequences with

http://www.jcat.de/

to check if the codon optimization in E.coli introduce a great codon bias for expression in mammalian.

OF course, it depends also from the amount of protein that you need. If you need ug you can try also with a non optimized gene, that probably will result in lower expression level.

good luck

Manuele

In multi-domain proteins of eukaryotes, rare codons are sometimes there for a reason, i.e. slowing down translation to allow folding properly. Therefore removing the rare codons could have an effect in the original expression system but doesn't have to. It is not easy to predict, what will happen, but it's unlikely that it will not work at all. The effect on the expression level seen in E. coli for an optimized human gene is usually bigger than optimized vs. native sequence in the same eukaryotic cell line.