Illustration of an oestrogen receptor (yellow and purple, ribbon model) binding to specific sequences (genes) on a strand of DNA (deoxyribonuclease, helical, sphere model). Oestrogen receptors are a group of proteins found within cells that are activated by the hormone oestrogen. Once activated, some oestrogen receptors bind to certain genes and regulate their activity, for example activating them to begin the process of protein transcription.