Transcription initiation is a major regulatory step in eukaryotic gene expression. Co-activators establish transcriptionally competent promoter architectures and chromatin signatures to allow the formation of the pre-initiation complex (PIC), comprising RNA polymerase II (Pol II) and general transcription factors (GTFs). Many GTFs and co-activators are multisubunit complexes, in which individual components are organized into functional modules carrying specific activities. Recent advances in affinity purification and mass spectrometry analyses have revealed that these complexes often share functional modules, rather than containing unique components. This observation appears remarkably prevalent for chromatin-modifying and remodeling complexes. Here, we use the modular organization of the evolutionary conserved Spt-Ada-Gcn5 acetyltransferase (SAGA) complex as a paradigm to illustrate how co-activators share and combine a relatively limited set of functional tools.

转录起始是真核基因表达的主要调控步骤。共激活剂建立具有转录能力的启动子结构和染色质特征，以形成起始前复合物 (PIC)，包括 RNA 聚合酶 II (Pol II) 和一般转录因子 (GTF)。许多 GTF 和共激活剂是多亚基复合体，其中单个组件被组织成承载特定活动的功能模块。亲和纯化和质谱分析的最新进展表明，这些复合物通常共享功能模块，而不是包含独特的组件。这种观察对于染色质修饰和重塑复合物来说似乎非常普遍。这里，