In producing an E. coli plasmid to be an expression vector, an experimenter includes genes for selectable markers, a promoter for the expression of the introduced genes. She uses a cDNA sequence to ensure the insert contains no introns. The gene inserted is transcribed, but not translated. What sequence did she omit from the plasmid?

An expression vector assists in expressing the gene into an mRNA and then into a protein by the process of transcription and translation respectively. In order to develop an effective expression vector, it should possess various essential organism-specific sequences so that they can articulate the desired gene.

For the process of transcription, a promoter is required, in order to understand the expression of a specific gene a selectable marker is required. While in prokaryotes, an RBS or the ribosome binding sequence like a Shine Dalgarno sequence is needed on the mRNA copy to initiate the process of translation.

Thus, it can be concluded that the researcher has missed out on the ribosome binding sequence due to which translation has not taken place.