ðə pˈɜːpəs ʌv ðɪs tɛknˈiːk ɪz tʊ ˈænɐlˌaɪz ðɪ æktˈɪvᵻɾi əvə dʒˈiːn tɹænskɹˈɪpʃən pɹəmˈoʊɾɚ ɪn tˈɜːmz ʌv ɛkspɹˈɛʃən əvə sˌoʊkˈɔːld ɹᵻpˈoːɹɾɚ dʒˈiːn ˌʌndɚ ðə ɹˈɛɡjʊlətˌoːɹi kəntɹˈoʊl ʌv ðæt pɹəmˈoʊɾɚ ˈiːðɚɹ ɪn ɐ kwˈɔntᵻtˌeɪɾɪv mˈænɚ, ɪnvˈɑːlvɪŋ sˌʌm mˈɛʒɚɹ ʌv æktˈɪvᵻɾi, ɔːɹ kwˈɔlᵻtˌeɪɾɪvli ˌɔn vˈɜːsᵻz ˈɔf θɹuː vˌɪʒuːəlᵻzˈeɪʃən ʌv ɪts æktˈɪvᵻɾi ɪn dˈɪfɹənt sˈɛlz, tˈɪʃuːz, ɔːɹ ˈɔːɹɡənz.
The purpose of this technique is to analyze the activity of a gene transcription promoter (in terms of expression of a so-called reporter gene under the regulatory control of that promoter) either in a quantitative manner, involving some measure of activity, or qualitatively (on versus off) through visualization of its activity in different cells, tissues, or organs.