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.
--------
Question:  Free protein S deficiency in acute ischemic stroke .

Answer: protein S


Question:  Interestingly , VDR was able to bind to VDREs with high affinity and to fully activate transcription in intact yeast cells in the presence of the retinoid X receptor ( RXR ) .

Answer: retinoid X receptor


Question:  Molecular cloning of cDNAs encoding alpha - subunits of guanine nucleotide - binding regulatory proteins ( G - proteins ) has revealed the existence of nine species of alpha - subunits .

Answer:
G - proteins