This gene encodes a member of the cytochrome P45 superfamily of enzymes. The cytochrome P45 proteins are monooxygenases which catalyze many reactions involved in drug metabolism and synthesis of cholesterol; steroids and other lipids. This protein localizes to the endoplasmic reticulum and catalyzes the last steps of estrogen biosynthesis. Mutations in this gene can result in either increased or decreased aromatase activity; the associated phenotypes suggest that estrogen functions both as a sex steroid hormone and in growth or differentiation. Alternative promoter use and alternative splicing results in multiple transcript variants that have different tissue specificities. [provided by RefSeq; Dec 216]