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) the use of cDNAs, that are free of introns, as eukaryotic transgenes
D) an E. coli expression vector with a promoter sequence that binds RNA polymerase
E) a negative selectable marker to select against nonhomologous recombination events