Derbigny Wilbert A, Kim Seong K, Jang Hyung K, O'Callaghan Dennis J
Department of Microbiology and Immunology, Louisiana State University Health Sciences Center, 1501 Kings Highway, Shreveport, LA 71130-3932, USA.
Virus Res. 2002 Mar 20;84(1-2):1-15. doi: 10.1016/s0168-1702(01)00377-x.
The early 293 amino acid EICP22 protein (EICP22P) of equine herpesvirus 1 localizes within the nucleus and functions as an accessory regulatory protein (J. Virol. 68 (1994) 4329). Transient transfection assays indicated that although the EICP22P by itself only minimally trans-activates EHV-1 promoters, the EICP22P functions synergistically with the immediate-early protein (IEP) to enhance expression of EHV-1 early genes (J. Virol. 71 (1997) 1004). We previously showed that the EICP22 protein enhances the DNA-binding activity of the EHV-1 IEP and that it also physically interacts with the IEP (J. Virol. 74 (2000) 1425). In this communication, we employed transient trans-activation assays utilizing EICP22P deletion mutants to address whether the sequences required for EICP22P-IEP physical interactions are essential for EICP22P's ability to interact synergistically with the IEP. Assays employing various classes of the EHV-1 promoters fused to the chloramphenicol acetyl-transferase (CAT) reporter gene indicated that: (1) neither full length nor any of the EICP22P mutants tested was able to overcome repression of the IE promoter elicited by the IEP, (2) the full-length EICP22P interacted synergistically with the IEP to trans-activate the early and late promoters tested, and (3) all of the EICP22P mutants, including those that were able to physically interact with IEP and itself, failed to function synergistically with the IEP to trans-activate representative EHV-1 early and late promoters. The results suggest that EICP22P sequences required for its interaction with the IE protein are not sufficient to mediate its synergistic effect on the trans-activation function of the IEP. The possible explanations as to why sequences in addition to those that mediate EICP22P-IEP interaction and EICP22P self-interactions are essential for the synergistic function of EICP22P are discussed.
马疱疹病毒1型的早期293个氨基酸的EICP22蛋白（EICP22P）定位于细胞核内，并作为一种辅助调节蛋白发挥作用（《病毒学杂志》68(1994)4329）。瞬时转染试验表明，虽然EICP22P自身仅能微弱地反式激活EHV-1启动子，但EICP22P与即刻早期蛋白（IEP）协同发挥作用，增强EHV-1早期基因的表达（《病毒学杂志》71(1997)1004）。我们之前表明，EICP22蛋白增强了EHV-1 IEP的DNA结合活性，并且它还与IEP发生物理相互作用（《病毒学杂志》74(2000)1425）。在本通讯中，我们利用EICP22P缺失突变体进行瞬时反式激活试验，以探讨EICP22P与IEP物理相互作用所需的序列对于EICP22P与IEP协同作用的能力是否至关重要。使用与氯霉素乙酰转移酶（CAT）报告基因融合的各类EHV-1启动子进行的试验表明：（1）全长EICP22P以及所测试的任何EICP22P突变体均无法克服IEP对IE启动子的抑制作用，（2）全长EICP22P与IEP协同作用，反式激活所测试的早期和晚期启动子，（3）所有EICP22P突变体，包括那些能够与IEP及自身发生物理相互作用的突变体，均无法与IEP协同作用以反式激活代表性的EHV-1早期和晚期启动子。结果表明，EICP22P与IE蛋白相互作用所需的序列不足以介导其对IEP反式激活功能的协同效应。文中讨论了除介导EICP22P-IEP相互作用和EICP22P自身相互作用的序列外，其他序列对于EICP22P协同功能至关重要的可能原因。
