Mismatch Repair Detection, a novel method for DNA-variation detection, utilizes bacteria to detect mismatches by a change in expression of a marker gene. A portable data carrier has an interface for sending and receiving data, data memory for storing received content data, and payment validation memory for providing payment validation data to an external device. A plurality of lateral frame rods are adjustably mounted along the length of the parallel rods of the front and rear frames so that the lateral rods may be moved to different locations to better accommodate loads carried on the lateral rods of the cart. If the non-critical segment is transmissive, the firmware controls the DMD so light is discontinued.