RESUMEN
We studied the regulation of murine CD80, a gene whose basal transcriptional status was characterized by the presence of a stalled RNA polymerase II complex on the promoter-proximal region. Stimulus-induced activation of productive elongation involved a complex interplay of regulated events that included a synergy between ordered cofactor recruitment. This cascade of recruitments was initiated through the engagement of transcription factor NF-kappaB, leading to the temporal association of histone acetyltransferases and the consequent selective acetylation of a transcription start site downstream nucleosome. This in turn culminated into the nucleosomal association of Brd4-associated P-TEFb, a protein complex containing kinase specific for serine 2 of Rbp 1, the largest subunit of the carboxyl-terminal domain of RNA polymerase II. The consequent phosphorylation of serine 2 residues in CTD by CDK9 in the P-TEFb complex then facilitated escape of polymerase II into the productive elongation phase. Thus, the cooperative mechanisms that integrate between independent pathways characterize regulation of the elongation step of transcription, thereby providing another level at which specificity of gene regulation can be achieved.
Asunto(s)
Regulación de la Expresión Génica , ARN Polimerasa II/metabolismo , Animales , Antígeno B7-1/química , Antígeno B7-1/metabolismo , Antígenos CD40/biosíntesis , Quinasa 9 Dependiente de la Ciclina/metabolismo , Ratones , Modelos Biológicos , Modelos Genéticos , FN-kappa B/metabolismo , Nucleosomas/metabolismo , Fosforilación , Factor B de Elongación Transcripcional Positiva/metabolismo , Regiones Promotoras Genéticas , Regulación hacia ArribaRESUMEN
The mode of regulation of class II genes that lack the known core promoter elements is presently unclear. Here, we studied one such example, the murine CD80 gene. An unusual mechanism was revealed wherein the pre-initiation complex (PIC) first assembled on an upstream, NF-kappaB enhancer element. Notably, this assembly occurred independent of contributions from the core promoter domain, and resulted in a PIC that was competent for transcription initiation. Positioning was subsequently achieved by exploiting the intrinsic architecture of the promoter, by virtue of which the tethered PIC was spatially juxtaposed with the transcription initiation site. Bridging interactions then ensued, through protein-protein contacts, which then enabled the elongation phase of CD80 transcription.