title: RNase HI Is Essential for Survival of Mycobacterium smegmatis.
abstract: RNases H are involved in the removal of RNA from RNA/DNA hybrids. Type I RNases H are thought to recognize and cleave the RNA/DNA duplex when at least four ribonucleotides are present. Here we investigated the importance of RNase H type I encoding genes for model organism Mycobacterium smegmatis. By performing gene replacement through homologous recombination, we demonstrate that each of the two presumable RNase H type I encoding genes, rnhA and MSMEG4305, can be removed from M. smegmatis genome without affecting the growth rate of the mutant. Further, we demonstrate that deletion of both RNases H type I encoding genes in M. smegmatis leads to synthetic lethality. Finally, we question the possibility of existence of RNase HI related alternative mode of initiation of DNA replication in M. smegmatis, the process initially discovered in Escherichia coli. We suspect that synthetic lethality of double mutant lacking RNases H type I is caused by formation of R-loops leading to collapse of replication forks. We report Mycobacterium smegmatis as the first bacterial species, where function of RNase H type I has been found essential.
authors.affiliation: Institute of Medical Biology, Polish Academy of Sciences, Lodz, Poland.
authors.forename: Alina E
authors.initials: AE
authors.lastname: Minias
authors.affiliation: Institute of Medical Biology, Polish Academy of Sciences, Lodz, Poland.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Brzostek
authors.affiliation: Institute of Medical Biology, Polish Academy of Sciences, Lodz, Poland.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Korycka-Machala
authors.affiliation: Department of Immunoparasitology, University of Lodz, Lodz, Poland.
authors.forename: Bozena
authors.initials: B
authors.lastname: Dziadek
authors.affiliation: Department of Teacher Training and Biodiversity Studies, University of Lodz, Lodz, Poland.
authors.forename: Piotr
authors.initials: P
authors.lastname: Minias
authors.affiliation: Department of Microbiology, University of Texas Health Center at Tyler, Tyler, Texas, United States of America.
authors.forename: Malini
authors.initials: M
authors.lastname: Rajagopalan
authors.affiliation: Department of Microbiology, University of Texas Health Center at Tyler, Tyler, Texas, United States of America.
authors.forename: Murty
authors.initials: M
authors.lastname: Madiraju
authors.affiliation: Institute of Medical Biology, Polish Academy of Sciences, Lodz, Poland.
authors.forename: Jaroslaw
authors.initials: J
authors.lastname: Dziadek
mesh_terms: D000595:Amino Acid Sequence / Q000235:genetics; D004261:DNA Replication / Q000235:genetics*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D016680:Genome, Bacterial; D059765:Homologous Recombination / Q000235:genetics; D020102:Mycobacterium smegmatis / Q000201:enzymology / Q000235:genetics*; D016914:Ribonuclease H / Q000235:genetics*
chemical_list: D016914:Ribonuclease H; C078856:ribonuclease HI