CmR

CmR is a common shorthand in molecular biology for a chloramphenicol resistance marker, typically associated with a gene that encodes chloramphenicol acetyltransferase (CAT). The enzyme inactivates chloramphenicol by acetylation, allowing bacteria carrying the CmR marker to grow in the presence of the antibiotic. In practice, CmR provides a selectable phenotype when transformed cells are cultured on media containing chloramphenicol.

The strength of CmR-based selection depends on factors such as the promoter used to drive CAT expression, plasmid copy number, host organism, and the chloramphenicol concentration chosen for selection. CmR markers have been widely used in cloning and recombinant DNA experiments, especially in bacterial systems, and often appear alongside other selectable markers to enable multi-plasmid or multi-gene strategies. Variants may involve different promoters, codon optimization, or plasmid backbones to suit specific hosts or experimental designs.

Safety and regulatory considerations are important when working with chloramphenicol resistance. Chloramphenicol is an antibiotic with significant toxicity in humans, including rare but serious adverse effects, and its use as a selection marker is subject to regulatory restrictions in many jurisdictions. Researchers must follow institutional biosafety guidelines, obtain necessary approvals, and ensure proper waste disposal and handling.

See also: chloramphenicol acetyltransferase, cat gene, antibiotic resistance, plasmid vector, selectable marker.