Seneca S, Punyammalee B, Sureau A, Perbal B, Dvorák M, Crabeel M
Erfelijheidsleer en Microbiologie, Vrije Universiteit Brussel, Research Institute Ceria-Coovi, Belgium.
Oncogene. 1993 Sep;8(9):2335-42.
We have shown previously that c-myb expressed in the yeast S. cerevisiae mediated efficient transcriptional activation of reporter genes designed with specific Myb Recognition Elements (MRE's), confirming that this proto-oncogene is able to function as a regulator of transcription in that heterologous context. Here we show that in yeast, as in higher eucaryotic cells, the central domain of c-Myb displays transactivating capacity. In yeast, however, the carboxy-terminal region, defined as a negative regulatory domain in higher cells, activates transcription as well and appears to be a more potent transactivating domain than the central domain itself. Within this region two domains, namely C1 and C2, have been defined that contribute about equally to the activity of the carboxy-terminal region. C1 spans the sequences missing in AMV v-myb while C2, which contains the leucine-zipper motif is specifically absent in the E26 v-myb in addition to C1. The c-Myb DNA-binding domain itself has no effect on the level of transcription in yeast. We also show that AMV v-Myb stimulates gene expression in yeast with about half the efficiency of full length c-Myb. The fact that the carboxy-terminal region either stimulates or inhibits transactivation properties of c-Myb, depending on the cellular context, stresses the participation of putative c-Myb partner proteins in Myb regulated processes and reopens the question of whether the oncogenic activation of c-myb is indeed due to the increased transactivation capacity of its onco derivatives.
我们之前已经表明，在酿酒酵母中表达的c-myb介导了对设计有特定Myb识别元件（MRE）的报告基因的高效转录激活，证实了这个原癌基因在该异源环境中能够作为转录调节因子发挥作用。在此我们表明，在酵母中，如同在高等真核细胞中一样，c-Myb的中央结构域具有反式激活能力。然而，在酵母中，在高等细胞中被定义为负调控结构域的羧基末端区域也能激活转录，并且似乎是比中央结构域本身更强有力的反式激活结构域。在这个区域内已经定义了两个结构域，即C1和C2，它们对羧基末端区域的活性贡献大致相等。C1跨越了禽成髓细胞瘤病毒（AMV）v-myb中缺失的序列，而C2除了包含C1缺失的序列外，还含有亮氨酸拉链基序，在E26 v-myb中特异性缺失。c-Myb的DNA结合结构域本身对酵母中的转录水平没有影响。我们还表明，AMV v-Myb刺激酵母中的基因表达，其效率约为全长c-Myb的一半。羧基末端区域根据细胞环境要么刺激要么抑制c-Myb的反式激活特性，这一事实强调了假定的c-Myb伴侣蛋白参与Myb调节过程，并重新开启了c-myb的致癌激活是否确实由于其致癌衍生物的反式激活能力增加的问题。
