These suspicions were confirmed LY2157299 inquirer through the observation that the overexpression of YpcP exonuclease suppressed the filamentous phenotype and overexpression of the exonuclease domain of PolI in these mutants. RNase HII/RNase HIII mutants showed temperature sensitive growth at 56.5��C. The O��Donell group confirmed the generation of double RNase HII/RNase HIII mutants in B. subtilis. RNase HII has been demonstrated as dispensable in E. coli, although this enzyme was initially considered essential. Using gene replacement through homologous recombination, we generated M. smegmatis mutants deficient in rnhB, suggesting that this gene is not essential for the survival of M. smegmatis. Therefore, either the function of the product of this gene is nonessential for cell survival in vitro or there are other genes in the mutant M. smegmatis genome whose products have overlapping functions with the mutated gene. The level of RNase HII substrates and the RNase HII deficiency affect genome stability in both eukaryotes and prokaryotes. In B. subtilis, the RNase HII/RNaseHIII/YpcP-deficient mutant displayed a filamentous phenotype, and this phenotype was suppressed through the overexpression of either the deleted genes or the 5��-3�� exonuclease domain of PolI. This phenotype resulted from the induced SOS response, which, in turn, might have resulted from the accumulation of unprocessed Okazaki fragments. The deletion of the 5��-3�� exonuclease domain of PolI in E. coli, which is primarily involved in the removal of Okazaki fragments in the absence of DNA damaging agents, increased the mutation rate in terms of frameshift and duplication mutations. It has also been suggested that persisting Okazaki primers destabilize tetranucleotide repeats in H. influenzae. This phenotype was associated with the deletion of RNase HI or the Klenow domain of PolI. The deletion of RNase H2 increased the mutation rate in budding yeast. A recent study showed that short, 2�C5 bp deletions observed in budding yeast mutants defective for RNase H2 result from topoisomerase I activity, and the deletion of topoisomerase I in RNase H2 mutants restored the mutation rate associated with these changes in the wild type. Notably, the rates for mutations other than 2�C5 bp deletions were not restored to the wild type in double the RNase H2/topoisomerase I mutant. These authors speculated that the increased mutation rate corresponded to the 10% decline in MMR efficiency. The hypothesis that ribonucleotides embedded within DNA act as a strand discrimination factor during MMR has been confirmed in eukaryotes. It has been shown that yeast DNA polymerase �� bypasses a single rNTP present within the DNA template, and the presence of ribonucleotides in the template delays bacterial replisome progression 4�C30-fold. Notably, mouse embryos deficient in RNase H2 show arrested development and display an increased number of ribonucleotides in the genomic DNA. Thus, ribonucleotides embedded within DNA duplex might constitute a barrier for FG-4592 HIF inhibitor replication fork progression. While this barrier is impossible to circumvent in higher eukaryotes, based on the essentiality of RNase H, in yeast, the double deletion of RNase H1 and RNase H2 sensitizes the cells to replication stress-inducing agents, such as HU and methyl methanesulfonate ; however, increased HU susceptibility after single RNase H2 deletion has been observed. Additionally, RNase H deletion induces the constant activation of post-replication repair, although the mechanisms of this phenomenon are poorly understood. Primary phenotypic analysis of the growth rate and cell morphology showed that ��rnhB M. smegmatis mutants exhibit growth similar to the wild-type strain, suggesting that ribonucleotides incorporated within DNA double helix after rnhB deletion do not constitute a barrier for replication fork progression.