For 10 points, name this organelle surrounding the nucleus that comes in "smooth" and "rough" varieties.
CASQ2 is the cardiac form of a protein that can be found in one type of this organelle; that protein is calsequestrin. Lysine, aspartic acid, glutamic acid, and leucine form a retention sequence in this organelle known as KDEL. Vesicles that are leaving this organelle are tagged with the protein COPII. Though not the Golgi apparatus, this organelle can contain flattened areas known as cisternae, and a type of this organelle is continuous with the double membrane of the nucleus. One version of this organelle named for its outer appearance is involved in lipid and carbohydrate metabolism. For 10 points, name this organelle surrounding the nucleus that comes in "smooth" and "rough" varieties.
CASQ2 is the cardiac form of a protein that can be found in one type of this organelle; that protein is calsequestrin.
endoplasmic reticulum [or ER; accept sarcoplasmic reticulum or SR before "lysine"]