Xist (X-inactive specific transcript) is a non-coding RNA transcribed from the X chromosome of the placental mammals that acts as a major effector of the X-inactivation process.[5] It is a component of the Xic – X-chromosome inactivation centre[6] – along with two other RNA genes (Jpx and Ftx) and two protein genes (Tsx and Cnbp2).[7]
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The Xist RNA, a large (17 kb in humans)[8] transcript, is expressed on the inactive chromosome and not on the active one. It is processed in a similar way to mRNAs, through splicing and polyadenylation. However, it remains untranslated. It has been suggested that this RNA gene evolved at least partly from a protein-coding gene that became a pseudogene.[9] The inactive X chromosome is coated with this transcript, which is essential for the inactivation.[10] X chromosomes lacking Xist will not be inactivated, while duplication of the Xist gene on another chromosome causes inactivation of that chromosome.[11]
The human Xist gene was discovered by Andrea Ballabio through a cDNA library screening and then characterized in collaboration with Carolyn J. Brown and Hunt Willard.[12][13]