X antigen family member 1B (also somewhat ambiguously called XAGE-1) is a protein that in humans is encoded by the XAGE1B gene. The XAGE1B gene encodes a protein which is typically identical to the protein encoded by its paralog, XAGE1A. This shared protein is often referred to as XAGE-1, when not specifying the origin gene. This gene is a member of the XAGE subfamily, which belongs to the GAGE family. The GAGE genes are expressed in a variety of tumors and in some fetal and reproductive tissues. This gene is strongly expressed in Ewing's sarcoma, alveolar rhabdomyosarcoma and normal testis. The protein encoded by this gene contains a nuclear localization signal and shares a sequence similarity with other GAGE/PAGE proteins. Because of the expression pattern and the sequence similarity, this protein also belongs to a family of CT (cancer-testis) antigens. Alternative splicing of this gene generates 3 transcript variants, and one of which includes 2 transcripts generated from alternate transcription initiation sites.
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