Different mechanisms participate in the R-dependent activity of the R2R3 MYB transcription factor C1
Different mechanisms participate in the R-dependent activity of the R2R3 MYB transcription factor C1
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DOI：
10.1074/jbc.m407845200
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发表时间：
2004-11-12
影响因子：
4.8
通讯作者：
Grotewold, E
中科院分区：
文献类型：
--
作者：
Hernandez, JM;Heine, GF;Grotewold, E
R2R3 MYB 转录因子 C1 需要碱性螺旋-环-螺旋因子 R 作为玉米花青素基因转录的重要共激活因子。相比之下，R2R3 MYB 蛋白 P1 独立于 R 激活 C1 调节基因的子集。用 C1 氨基酸替换 P1 中的六个氨基酸产生 P1*，其对 C1 调节和 P1 调节基因的活性分别是 R 依赖性或 R 增强。我们将 P1* 与各种启动子结合使用，揭示了 R 功能的两种机制。在仅包含 C1/P1 结合位点的合成启动子上，R 是 C1 的重要共激活剂。 R 的这种功能不太可能仅仅是 C1 DNA 结合亲和力增加的结果，因为与 P1 相比，以更高亲和力结合 DNA 的 C1 突变体的转录活性仍然依赖于 R。在酵母和玉米细胞中，C1 与酵母 Gal4 DNA 结合域融合的差异转录活性表明，R 的部分功能是解除 C1 的植物特异性抑制剂的作用。 R 的第二个功能除了 C1/P1 DNA 结合位点外还需要顺式调控元件，以实现 R 增强的 a1 转录。我们假设 R 在这种模式下通过结合或招募额外的因子到几个花青素基因启动子中保守的花青素调节元件来发挥作用。总之，这些发现提出了一个模型，其中与共激活剂的组合相互作用使具有非常相似的 DNA 结合偏好的 R2R3 MYB 因子能够在体内区分靶基因。
The R2R3 MYB transcription factor C1 requires the basic helix-loop-helix factor R as an essential co-activator for the transcription of maize anthocyanin genes. In contrast, the R2R3 MYB protein P1 activates a subset of the C1-regulated genes independently of R. Substitution of six amino acids in P1 with the C1 amino acids results in P1*, whose activity on C1-regulated and P1-regulated genes is R-dependent or R-enhanced, respectively. We have used P1* in combination with various promoters to uncover two mechanisms for R function. On synthetic promoters that contain only C1/P1 binding sites, R is an essential co-activator of C1. This function of R is unlikely to simply be the result of an increase in the C1 DNA-binding affinity, since transcriptional activity of a C1 mutant that binds DNA at a higher affinity, comparable with P1, remains R-dependent. The differential transcriptional activity of C1 fusions with the yeast Gal4 DNA-binding domain in yeast and maize cells suggests that part of the function of R is to relieve C1 from a plant-specific inhibitor. A second function of R requires cis-regulatory elements in addition to the C1/P1 DNA-binding sites for R-enhanced transcription of a1. We hypothesize that R functions in this mode by binding or recruiting additional factors to the anthocyanin regulatory element conserved in the promoters of several anthocyanin genes. Together, these findings suggest a model in which combinatorial interactions with co-activators enable R2R3 MYB factors with very similar DNA binding preferences to discriminate between target genes in vivo.