Given the task definition and input, reply with output. In this task, you are given a sentence. You are expected to recognize the name of gene or protein. Although there might be several correct answers, you need to write one of them.

In K562 cells , using the bicistronic vector , selection with colchicine led to at least 20 - fold higher expression of the MDR1 gene product than did selection with G418 , suggesting that the stringent MDR1 selection system is very efficient for obtaining overexpression of foreign genes .
MDR1 gene product