Two pathways of transcription termination, factor-independent and -dependent, 
exist in bacteria. The latter pathway operates on nascent transcripts that are 
not simultaneously translated and requires factors Rho, NusG, and NusA, each of 
which is essential for viability of WT Escherichia coli. NusG and NusA are also 
involved in antitermination of transcription at the ribosomal RNA operons, as 
well as in regulating the rates of transcription elongation of all genes. We 
have used a bisulfite-sensitivity assay to demonstrate genome-wide increase in 
the occurrence of RNA-DNA hybrids (R-loops), including from antisense and 
read-through transcripts, in a nusG missense mutant defective for Rho-dependent 
termination. Lethality associated with complete deficiency of Rho and NusG (but 
not NusA) was rescued by ectopic expression of an R-loop-helicase UvsW, 
especially so on defined growth media. Our results suggest that factor-dependent 
transcription termination subserves a surveillance function to prevent 
translation-uncoupled transcription from generating R-loops, which would block 
replication fork progression and therefore be lethal, and that NusA performs 
additional essential functions as well in E. coli. Prevention of R-loop-mediated 
transcription-replication conflicts by cotranscriptional protein engagement of 
nascent RNA is emerging as a unifying theme among both prokaryotes and 
eukaryotes.