The present invention provides in general an artificial cell, an isolated mutant ER.alpha., an isolated polynucleotide encoding the mutant ER.alpha., a method for quantitatively analyzing an activity for transactivation of a reporter gene by a test ER.alpha., a method for screening a mutant ligand dependent transcriptional factor, a method for evaluating an activity for transactivation of a reporter gene by a test ER.alpha., a method for screening a compound useful for treating a disorder of a mutant ER.alpha., a pharmaceutical agent useful for treating an estrogenic disorder of a mutant ER.alpha., use of the mutant ER.alpha., a method for diagnosing a genotype of a polynucleotide encoding a test ER.alpha., a method for diagnosing a genotype of a polynucleotide encoding a test ER.alpha. and a method for diagnosing a phenotype of a test ER.alpha..