Detailed Instructions: 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: No evidence for the existence of a specific progesterone receptor in human mononuclear leukocytes was obtained as judged by the results of competition experiments where a progesterone receptor - specific ligand [ 3H ] Org 2058 was used .
A:
progesterone receptor