Efficient production of eukaryotic proteins in E. coli may require all of the following except?
a.altered codon usage within the heterologous sequences to approximate the codon bias in E. coli
b.an E. coli expression vector with a Shine- Dalgarno sequence for efficient translation
c.a negative selectable marker to select against nonhomologous recombination events
d.The use of cDNAs as eukaryotic transgenes an E. coli expression vector with a promoter sequence that binds RNA polymerase D