CIITA（class II major histocompatibility complex transactivator），癌症关联基因，基因ID：4261，该基因编码一个具有酸性转录激活结构域、4个LRRs（富含亮氨酸重复序列）和GTP结合结构域的蛋白质该蛋白位于细胞核内，是Ⅱ类主要组织相容性复合物基因转录的正调控因子，被称为这些基因表达的“主控因子”该蛋白还结合GTP，并利用GTP结合促进自身运输到细胞核一旦进入细胞核，它就不会与DNA结合，而是利用一种内在的乙酰转移酶（AT）活性，以一种类似于辅活化剂的方式起作用。该基因突变与裸淋巴细胞综合征Ⅱ型（也称为遗传性mhcⅡ类缺陷或hlaⅡ类缺陷的联合免疫缺陷）、类风湿关节炎易感性增加、多发性硬化和可能的心肌梗死有关。已经发现了一些编码不同亚型的转录变体。[ RefSeq，2013月11日]This gene encodes a protein with an acidic transcriptional activation domain， 4 LRRs (leucine-rich repeats) and a GTP binding domain. The protein is located in the nucleus and acts as a positive regulator of class II major histocompatibility complex gene transcription， and is referred to as the "master control factor" for the expression of these genes. The protein also binds GTP and uses GTP binding to facilitate its own transport into the nucleus. Once in the nucleus it does not bind DNA but rather uses an intrinsic acetyltransferase (AT) activity to act in a coact。