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.

Q:  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 .

A: MDR1 gene product
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Q:  A selective transcriptional induction system for mammalian cells based on Gal4 - estrogen receptor fusion proteins .

A: estrogen receptor
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Q:  Blockade of T cell activation using a surface - linked single - chain antibody to CTLA - 4 ( CD152 ) .

A:
CTLA - 4
****