Question: How do R-loops affect replication forks, and which enzyme helps?

Context:
 detected in cancer cells.", "The multiple cleavage sites on the R-loop substrate match the priming sites observed in vivo, suggesting that RNase MRP alone is capable of generating virtually all of the leading-strand replication primers.", "Mechanisms of primer RNA synthesis and D-loop/R-loop-dependent DNA replication in Escherichia coli.", "Alternative oriC-independent modes of replication initiation are possible, one of which is constitutive stable DNA replication (cSDR) from transcription-associated RNA-DNA hybrids or R-loops.", "Our results suggest that Top1 execute this function by suppressing the formation of DNA-RNA hybrids during transcription, these so-called R-loops interfering with the progression of replication forks.", "Critical role of R-loops in processing replication blocks.", "The possibility that RecG regulates the initiation of a unique mode of DNA replication, oriC-independent constitutive stable DNA replication, by its activity in resolving R-loops is discussed.", "Competition between the RNA transcript and the nontemplate DNA strand during R-loop formation in vitro: a nick can serve as a strong R-loop initiation site.", "More importantly, we then show that R-loop formation causes DNA replication fork stalling, and that this in fact underlies the effects of R loops on genomic stability. ", "Consistent with this hypothesis, the 3' ends of the mitochondrial R-loop formed by in vitro transcription are located close to the initiation sites of the mitochondrial DNA replication. ", "A hybrid G-quadruplex structure formed between RNA and DNA explains the extraordinary stability of the mitochondrial R-loop.", "Previous studies have shown that the newly synthesized primers form a stable and persistent RNA-DNA hybrid, a R-loop, near the leading-strand origin of DNA replication. ", "Escherichia coli rnhA mutants devoid of RNase HI exhibit constitutive stable DNA replication, cSDR, which is thought to be initiated from R-loops stabilized in the absence of RNase HI. "]
 detected in cancer cells.", "The multiple cleavage sites on the R-loop substrate match the priming sites observed in vivo, suggesting that RNase MRP alone is capable of generating virtually all of the leading-strand replication primers.", "Mechanisms of primer RNA synthesis and D-loop/R-loop-dependent DNA replication in Escherichia coli.", "Alternative oriC-independent modes of replication initiation are possible, one of which is constitutive stable DNA replication (cSDR) from transcription-associated RNA-DNA hybrids or R-loops.", "Our results suggest that Top1 execute this function by suppressing the formation of DNA-RNA hybrids during transcription, these so-called R-loops interfering with the progression of replication forks.", "Critical role of R-loops in processing replication blocks.", "The possibility that RecG regulates the initiation of a unique mode of DNA replication, oriC-independent constitutive stable DNA replication, by its activity in resolving R-loops is discussed.", "Competition between the RNA transcript and the nontemplate DNA strand during R-loop formation in vitro: a nick can serve as a strong R-loop initiation site.", "More importantly, we then show that R-loop formation causes DNA replication fork stalling, and that this in fact underlies the effects of R loops on genomic stability. ", "Consistent with this hypothesis, the 3' ends of the mitochondrial R-loop formed by in vitro transcription are located close to the initiation sites of the mitochondrial DNA replication. ", "A hybrid G-quadruplex structure formed between RNA and DNA explains the extraordinary stability of the mitochondrial R-loop.", "Previous studies have shown that the newly synthesized primers form a stable and persistent RNA-DNA hybrid, a R-loop, near the leading-strand origin of DNA replication. ", "Escherichia coli rnhA mutants devoid of RNase HI exhibit constitutive stable DNA replication, cSDR, which is thought to be initiated from R-loops stabilized in the absence of RNase HI. "]

Answer: R-loop formation causes DNA replication fork stalling, and this underlies the effects of R loops on genomic stability. The enzyme Top1 helps by suppressing the formation of DNA-RNA hybrids during transcription, which are the R-loops interfering with the progression of replication forks.