Burdick, J. T. | bioRxiv Science

bioRxiv2023

Guanine quadruplexes mediate mitochondrial RNA polymerase pausing

The information content within nucleic acids extends beyond the primary sequence to include secondary structures with functional roles in cells. Guanine-rich sequences form structures called guanine quadruplexes (G4) that result from non-canonical base pairing between guanine residues. These stable structures are enriched in gene promoters and have been correlated with the locations of RNA polymerase II pausing (Pol II). While promoter-proximal RNA polymerase pausing regulates gene expression, the effects of guanine quadruplexes on gene transcription have been less clear. We determined the pattern of mitochondrial RNA polymerase (mtRNAP) pausing in human fibroblasts and found that it pauses over 400 times on the mitochondrial genome. We identified quadruplexes as a mediator of mtRNAP pausing and show that stabilization of quadruplexes impeded transcription by mtRNAP. Gene products encoded by the mitochondrial genome are required for oxidative phosphorylation and the decreased transcription by mtRNAP resulted in lower expression of mitochondrial genes and significantly reduced ATP generation. Energy from mitochondria is essential for transport function in renal epithelia, and impeded mitochondrial transcription inhibits transport function in renal proximal tubule cells. These results link formation of guanine quadruplex structures to regulation of mtRNAP elongation and mitochondrial function.

molecular biology↗

bioRxiv2022

A transcriptional mechanism involving R-loop, m6A modification and RNA abasic sites regulates an enhancer RNA of APOE.

The DNA genetic code and the RNA regulatory code determine phenotypes from gene expression to disease susceptibility. DNA sequence variants lead to phenotypic differences among individuals, while within an individual, RNA dynamically confers cell identity and responds to cellular and environmental signals. To provide regulation for different cell types and conditions, the nucleotides of RNA are modified by hundreds of chemical reactions, and RNA folds into innumerable shapes. To decipher the RNA regulatory code is to understand how RNA sequence and structure respond to cellular needs. Here, we deciphered one part of the RNA code where RNA abasic sites in R-loops regulate transcription by pausing RNA polymerase II. We uncovered an enhancer RNA, AANCR, that regulates the transcription and expression of APOE. When AANCR is folded into an R-loop, which is then modified by N6-adenine methylation and N-glycosidic cleavage, it is a partially transcribed nonfunctional enhancer and APOE is not expressed. In contrast, in some cell types and under stress, AANCR does not form a stable R-loop as its sequence is not modified, so it is transcribed into a full-length enhancer that promotes APOE expression. By genetic analysis, we confirmed that AANCR regulates APOE expression. DNA sequence variants in AANCR are associated with APOE expression and also with Alzheimers disease. Our data show that DNA and RNA sequence and structure jointly regulate gene expression that influence disease risk. HighlightsO_LIm6A, RNA abasic sites and R-loops jointly regulate transcription by pausing RNA Polymerase II. C_LIO_LIAn enhancer RNA regulates APOE expression. C_LIO_LIEnhancer RNA of APOE modifies susceptibility to Alzheimers disease. C_LI

molecular biology↗