Final answer:
To express a cow transgene in a bacterial cell, the expression vector must include a bacterial promoter, ribosome binding site, selectable marker, origin of replication, and potentially a signal sequence. Eukaryotic promoters should not be used as bacteria cannot process them.
Step-by-step explanation:
When expressing a cow transgene in a bacterial cell using an expression vector, several essential elements must be included for successful transcription and translation of the gene into a functional protein. These elements typically include a bacterial promoter, which is critical for initiating transcription in the prokaryotic host, a ribosome binding site (RBS) for the initiation of translation, a selectable marker gene to identify transformed cells, and an origin of replication for the plasmid to be replicated within the bacterial cell. Some expression vectors may also require a signal sequence for the proper export of the protein from the bacterial cell if the target protein is to be secreted. Furthermore, to ensure proper folding and activity of the protein, which might be specifically adapted to eukaryotic post-translational modifications, appropriate coding sequences may need to be included or optimized for prokaryotic use. It's important to consider that a eukaryotic promoter should not be used because bacteria are unable to recognize and process these eukaryotic signals effectively.