Monkey Kidney Cells with mEmerald-PMP and mRuby-ER
The endoplasmic reticulum (ER) belongs to a protein sorting pathway. Most of endoplasmic reticulum resident proteins are preserved in the endoplasmic reticulum through a retention motif. This motif is comprised of four amino acids at the end of the protein sequence. KDEL (lys-asp-glu-leu) is the most prevalent retention sequence, though variation on KDEL does occur and alternative sequences can also cause endoplasmic reticulum retention, though it has not been proven that such variation can give way to sub-endoplasmic reticulum localizations. In the digital video sequence in this section, African green monkey kidney epithelial cells (BS-C-1 line) can be seen expressing mApple fused to the endoplasmic reticulum and mEmerald fused to peroxisomes.
The green fluorescent protein employed in this video sequence, mEmerald, was developed from an enhanced form of Aequorea GFP. mEmerald is relatively bright and photostable, but exhibits a fast photobleaching component that can be problematic in certain applications. The red fluorescent protein mRuby is a derivative of eqFP611, a tetrameric far-red fluorescent protein. Similar to eqFP611, mRuby displays a large Stokes shift, but mRuby also benefits from enhanced brightness.