pDsRed-Monomer-N1 is a mammalian expression vector that encodes DsRed-Monomer (DsRed.M1), a monomeric mutant derived from the tetrameric Discosoma sp. red fuorescent protein DsRed. DsRed-Monomer contains forty-fve amino acid substitutions (listed on page 2). When DsRed-Monomer is expressed in mammalian cell cultures, red fuorescent cells can be detected by either fuorescence microscopy or fow cytometry 12–16 hr after transfection (DsRed-Monomer excitation and emission maxima = 557 nm and 592 nm, respectively). The DsRed-Monomer coding sequence is human codon-optimized for high expression in mammalian cells.