A gene that makes a protein called calreticulin, which is involved in many cell functions. Calreticulin helps control the amount of calcium that is stored in cells. This is thought to play a role in the control of gene activity, cell growth and movement, the attachment of cells to one another, and cell death. Mutated (changed) forms of the CALR gene have been found in some types of blood conditions, including essential thrombocythemia and primary myelofibrosis.