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