Instituto de Biología Funcional y Genómica, CSIC-USAL, Salamanca, Spain.
Department of Biological Science. Wayne State University. Detroit, MI 48202, USA.
Nucleic Acids Res. 2019 Sep 26;47(17):8975-8987. doi: 10.1093/nar/gkz597.
Gene loops are formed by the interaction of initiation and termination factors occupying the distal ends of a gene during transcription. RNAPII is believed to affect gene looping indirectly owing to its essential role in transcription. The results presented here, however, demonstrate a direct role of RNAPII in gene looping through the Rpb4 subunit. 3C analysis revealed that gene looping is abolished in the rpb4Δ mutant. In contrast to the other looping-defective mutants, rpb4Δ cells do not exhibit a transcription termination defect. RPB4 overexpression, however, rescued the transcription termination and gene looping defect of sua7-1, a mutant of TFIIB. Furthermore, RPB4 overexpression rescued the ssu72-2 gene looping defect, while SSU72 overexpression restored the formation of gene loops in rpb4Δ cells. Interestingly, the interaction of TFIIB with Ssu72 is compromised in rpb4Δ cells. These results suggest that the TFIIB-Ssu72 interaction, which is critical for gene loop formation, is facilitated by Rpb4. We propose that Rpb4 is promoting the transfer of RNAPII from the terminator to the promoter for reinitiation of transcription through TFIIB-Ssu72 mediated gene looping.
基因环是由起始和终止因子在转录过程中占据基因末端相互作用形成的。由于 RNAPII 在转录中的重要作用，人们认为它会间接地影响基因环的形成。然而，这里呈现的结果表明，RNAPII 通过其 Rpb4 亚基直接参与基因环的形成。3C 分析表明，rpb4Δ 突变体中的基因环消失。与其他基因环缺陷突变体不同，rpb4Δ 细胞没有表现出转录终止缺陷。然而，RPB4 的过表达挽救了 sua7-1（TFIIB 的突变体）的转录终止和基因环缺陷。此外，RPB4 的过表达挽救了 ssu72-2 的基因环缺陷，而 SSU72 的过表达则恢复了 rpb4Δ 细胞中基因环的形成。有趣的是，rpb4Δ 细胞中 TFIIB 与 Ssu72 的相互作用受损。这些结果表明，TFIIB-Ssu72 相互作用对于基因环的形成至关重要，而这种相互作用是由 Rpb4 促进的。我们提出，Rpb4 通过 TFIIB-Ssu72 介导的基因环形成，促进 RNAPII 从终止子转移到启动子，以重新起始转录。
