Exoproteome analysis of Pseudomonas aeruginosa response to high alkane stress.

Microbial biodegradation serves as an effective approach to treat oil pollution. However, the application of such methods for the degrading long-chain alkanes still encounters significant challenges. Comparative proteomics has extensively studied the intracellular proteins of bacteria that degrade short- and medium-chain alkanes, but the role and mechanism of extracellular proteins in many microorganism remain unclear. To enhance our understanding of the roles of extracellular proteins in the adaptation to long-chain alkanes, a label-free LC-MS/MS strategy was applied for the relative quantification of extracellular proteins of Pseudomonas aeruginosa SJTD-1-M (ProteomeXchange identifier PXD014638). 444 alkane-sentitive proteins were acquired and their cell localization analysis was performed using the Pseudomonas Genome Database. Among them, 111 proteins were found to be located in extracellular or Outer Membrane Vesicles (OMVs). The alkane-induced abundance of 11 extracellular or OMV target proteins was confirmed by parallel reaction monitoring (PRM). Furthermore, we observed that the expression levels of three proteins (Pra, PA2815, and FliC) were associated with the carbon chain length of the added alkane in the culture medium. The roles of these proteins in cell mobility, alkane emulsification, assimilation, and degradation were further discussed. OMVs were found to contain a number of enzymes involved in alkane metabolism, fatty acid beta-oxidation, and the TCA cycle, suggesting their potential as sites for facilitated alkane degradation. In this sense, this exoproteome analysis contributes to a better understanding of the role of extracellular proteins in the hydrocarbon treatment process.

Glycosidase-activated H2S donorsto enhance chemotherapy efficacy.

Hydrogen sulfide (H2S) plays a critical role in cancer biology. Herein, we developed a series of glycosidase-triggered hydrogen sulfide (H2S) donors by connecting sugar moieties (including glucose, galactose and mannose) to COS donors via a self-immolative spacer. In the presence of corresponding glycosidases, H2S was gradually released from these donors in PBS buffer with releasing efficiencies from 36 to 67 %. H2S release was also detected by H2S probe WSP-1 after treatment HepG2 cells with Man1. Cytotoxicities of these glycosylated H2S donors were evaluated against HepG2 by MTT assay. Among them, Man1 and Man2 exhibited an obvious reduction of cell viability in HepG2 cells, with cell viability as 37.6 % for 80 µM of Man. Consistently, significant apoptosis was observed in HepG2 cells after treatment with Man1 and Man2. Finally, We evaluated the potential of Man1 for combination therapy with doxorubicin. A synergistic effect was observed between Man1 and Doxorubicin in HepG2 and Hela cells. All these results indicated glycosidase-activated H2S donorshave promising potential for cancer therapy.

O-glycosylation of SARS-CoV-2 spike protein by host O-glycosyltransferase strengthens its trimeric structure.

Protein O-glycosylation, also known as mucin-type O-glycosylation, is one of the most abundant glycosylation in mammalian cells. It is initially catalyzed by a family of polypeptide GalNAc transferases (ppGalNAc-Ts). The trimeric spike protein (S) of SARS-CoV-2 is highly glycosylated and facilitates the virus's entry into host cells and membrane fusion of the virus. However, the functions and relationship between host ppGalNAc-Ts and O-glycosylation on the S protein remain unclear. Herein, we identify 15 O-glycosites and 10 distinct O-glycan structures on the S protein using an HCD-product-dependent triggered ETD mass spectrometric analysis. We observe that the isoenzyme T6 of ppGalNAc-Ts (ppGalNAc-T6) exhibits high O-glycosylation activity for the S protein, as demonstrated by an on-chip catalytic assay. Overexpression of ppGalNAc-T6 in HEK293 cells significantly enhances the O-glycosylation level of the S protein, not only by adding new O-glycosites but also by increasing O-glycan heterogeneity. Molecular dynamics simulations reveal that O-glycosylation on the protomer-interface regions, modified by ppGalNAc-T6, potentially stabilizes the trimeric S protein structure by establishing hydrogen bonds and non-polar interactions between adjacent protomers. Furthermore, mutation frequency analysis indicates that most O-glycosites of the S protein are conserved during the evolution of SARS-CoV-2 variants. Taken together, our finding demonstrate that host O-glycosyltransferases dynamically regulate the O-glycosylation of the S protein, which may influence the trimeric structural stability of the protein. This work provides structural insights into the functional role of specific host O-glycosyltransferases in regulating the O-glycosylation of viral envelope proteins.

Interplay between the bacterial protein deacetylase CobB and the second messenger c-di-GMP.

As a ubiquitous bacterial secondary messenger, c-di-GMP plays key regulatory roles in processes such as bacterial motility and transcription regulation. CobB is the Sir2 family protein deacetylase that controls energy metabolism, chemotaxis, and DNA supercoiling in many bacteria. Using an Escherichia coli proteome microarray, we found that c-di-GMP strongly binds to CobB. Further, protein deacetylation assays showed that c-di-GMP inhibits the activity of CobB and thereby modulates the biogenesis of acetyl-CoA. Interestingly, we also found that one of the key enzymes directly involved in c-di-GMP production, DgcZ, is a substrate of CobB. Deacetylation of DgcZ by CobB enhances its activity and thus the production of c-di-GMP. Our work establishes a novel negative feedback loop linking c-di-GMP biogenesis and CobB-mediated protein deacetylation.

Identification of sitagliptin binding proteins by affinity purification mass spectrometry.

Type 2 diabetes mellitus (T2DM) is recognized as a serious public health concern with increasing incidence. The dipeptidyl peptidase-4 (DPP-4) inhibitor sitagliptin has been used for the treatment of T2DM worldwide. Although sitagliptin has excellent therapeutic outcome, adverse effects are observed. In addition, previous studies have suggested that sitagliptin may have pleiotropic effects other than treating T2DM. These pieces of evidence point to the importance of further investigation of the molecular mechanisms of sitagliptin, starting from the identification of sitagliptin-binding proteins. In this study, by combining affinity purification mass spectrometry (AP-MS) and stable isotope labeling by amino acids in cell culture (SILAC), we discover seven high-confidence targets that can interact with sitagliptin. Surface plasmon resonance (SPR) assay confirms the binding of sitagliptin to three proteins, i. e., LYPLAL1, TCP1, and CCAR2, with binding affinities (K D) ranging from 50.1 µM to 1490 µM. Molecular docking followed by molecular dynamic (MD) simulation reveals hydrogen binding between sitagliptin and the catalytic triad of LYPLAL1, and also between sitagliptin and the P-loop of ATP-binding pocket of TCP1. Molecular mechanics Poisson-Boltzmann Surface Area (MMPBSA) analysis indicates that sitagliptin can stably bind to LYPLAL1 and TCP1 in active sites, which may have an impact on the functions of these proteins. SPR analysis validates the binding affinity of sitagliptin to TCP1 mutant D88A is ~10 times lower than that to the wild-type TCP1. Our findings provide insights into the sitagliptin-targets interplay and demonstrate the potential of sitagliptin in regulating gluconeogenesis and in anti-tumor drug development.

Targeted delivery of nitric oxide via a 'bump-and-hole'-based enzyme-prodrug pair.

The spatiotemporal generation of nitric oxide (NO), a versatile endogenous messenger, is precisely controlled. Despite its therapeutic potential for a wide range of diseases, NO-based therapies are limited clinically due to a lack of effective strategies for precisely delivering NO to a specific site. In the present study, we developed a novel NO delivery system via modification of an enzyme-prodrug pair of galactosidase-galactosyl-NONOate using a 'bump-and-hole' strategy. Precise delivery to targeted tissues was clearly demonstrated by an in vivo near-infrared imaging assay. The therapeutic potential was evaluated in both rat hindlimb ischemia and mouse acute kidney injury models. Targeted delivery of NO clearly enhanced its therapeutic efficacy in tissue repair and function recovery and abolished side effects due to the systemic release of NO. The developed protocol holds broad applicability in the targeted delivery of important gaseous signaling molecules and offers a potent tool for the investigation of relevant molecular mechanisms.

Piperazine-Coumarin based fluorescence probe with enhanced brightness and solubility for bio-thiol detection and esophageal carcinoma diagnosis.

The development of novel fluorescent dyes for bio-thiol is of great importance in biological, clinical and pharmaceutical sciences. Given the importance of bio-thiol anticipating in numerous physiological processes, there is a great need to construct fluorescent biosensors with high quality to detect them. Fluorophores, especially those used in bio-system, usually require high-quality properties such as high brightness, good water solubility, bio-compatible and photostability. Herein, we reported a novel fluorescent probe based on piperazine-coumarin scaffold with enhanced brightness and solubility. To further demonstrate the potential clinical applications, we performed living cell fluorescence image and human esophageal carcinoma diagnosis. The result indicated that we were able to distinguish pathological tissue from normal tissue by applying this probe. Thus, we hope this design will be helpful to develop high-quality fluorophores for clinical diagnosis.

Synthesis of difluoroalkylated 2-azaspiro[4.5]decane derivatives via copper-catalyzed difluoroalkylation/dearomatization of N-benzylacrylamides.

An efficient method for the synthesis of difluoroalkylated 2-azaspiro[4.5]decanes via copper-catalyzed difluoroalkylation of N-benzylacrylamides with ethyl bromodifluoroacetate has been established. The reaction experienced a tandem radical addition and dearomatizing cyclization process. In addition, the resultant products can be smoothly converted into a difluoroalkylated quinolinone and saturated spirocyclohexanone scaffold.

Photoactive NO hybrids with pseudo-zero-order release kinetics for antimicrobial applications.

Bacterial infection is a major threat to the health and life of humans due to the development of drug resistance, which is related to biofilm formation. Nitric oxide (NO) has emerged as an important factor in regulating biofilm formation. In order to harness the potential benefits of NO and develop effective antibacterial agents, we designed and synthesized a new class of NO hybrids in which the active scaffold benzothienoazepine was tagged with a nitroso group and further conjugated with quaternary ammoniums or phosphoniums. The temporal release of NO from these hybrids can be achieved by photoactivation. Interestingly, the NO release follows a pseudo-zero-order kinetics, which is easily determined by measuring the fluorescent benzothienoazepine or NO. Compared to the positive control ciprofloxacin, the NO hybrid with triphenyl phosphonium (TPP) exhibited more effective activity against S. aureus biofilm in darkness. Irradiation of the NO hybrid led to higher inhibition against S. aureus biofilm compared to the parental NO hybrid in darkness or the corresponding NO-released product, indicating the combined effect of NO and the NO-released product. Therefore, this new class of NO hybrids includes very promising antimicrobial agents and this work provides a new way for the design of highly effective antimicrobial agents.

Synthesis and Characterization of Hydrophilic Trityl Radical TFO for Biomedical and Biophysical Applications.

Tetrathiatriarylmethyl (TAM, trityl) radicals have found wide applications as spin probes/labels for EPR spectroscopy and imaging, and as polarizing agents for dynamic nuclear polarization. The high hydrophilicity of TAM radicals is essential for their biomedical applications. However, the synthesis of hydrophilic TAM radicals (e.g., OX063) is extremely challenging and has only been reported in the patent literature, to date. Herein, an efficient synthesis of a highly water-soluble TAM radical bis(8-carboxyl-2,2,6,6-tetramethylbenzo[1,2-d:4,5-d']bis([1,3]dithiol-4-yl)-mono-(8-carboxyl-2,2,6,6-tetrakis(2-hydroxyethyl)benzo[1,2-d:4,5-d']bis([1,3]dithiol-4-yl)methyl (TFO), which contains four additional hydroxylethyl groups, relative to the Finland trityl radical CT-03, is reported. Similar to OX063, TFO exhibits excellent properties, including high water solubility in phosphate buffer, low log P, low pKa , long relaxation times, and negligible binding with bovine serum albumin. On the other hand, TFO has a sharper EPR line and higher O2 sensitivity than those of OX063. Therefore, in combination with its facile synthesis, TFO should find wide applications in magnetic resonance related fields and this synthetic approach would shed new light on the synthesis of other hydrophilic TAM radicals.

Synthesis of Central Chirality-Containing Triarylmethanols and Triarylmethyl Radicals with Extraordinarily Stable Configurations.

Triarylmethanol adopts a propeller-shaped conformation with either right-handed (P) or left-handed (M) configuration. Herein, new triarylmethanols with two chiral centers were obtained via introduction of two cis-hydroxyl groups on the side chains, affording four stereoisomers. These four stereoisomers were easily separated by silica gel column chromatography into two pairs of propeller-shaped enantiomers, as shown by NMR and X-ray crystallographic studies. High-performance liquid chromatography (HPLC) studies showed that the configurations of the hydroxyl-bearing triarylmethanols are much more stable than those of the bulky tert-butyldimethylsilyl-protected precursors, inconsistent with the general strategy in which the steric repulsion is largely responsible for the configurational stability. Similarly, two hydroxyl-bearing tetrathiatriarylmethyl (TAM) radicals also exhibit excellent configurational stability and are thus separable by CS-HPLC into four stereoisomers. Interestingly, both helical chirality from triaryl group (M or P) and central chirality (R and S) on the side chain have little effect on their electron paramagnetic resonance properties. Our present study provides a new strategy to construct configurationally stable triaryl compounds and demonstrates that the side chain on TAM radicals is a new site for their structural modifications.

The Ser/Thr Protein Kinase Protein-Protein Interaction Map of M. tuberculosis.

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis, the leading cause of death among all infectious diseases. There are 11 eukaryotic-like serine/threonine protein kinases (STPKs) in Mtb, which are thought to play pivotal roles in cell growth, signal transduction and pathogenesis. However, their underlying mechanisms of action remain largely uncharacterized. In this study, using a Mtb proteome microarray, we have globally identified the binding proteins in Mtb for all of the STPKs, and constructed the first STPK protein interaction (KPI) map that includes 492 binding proteins and 1,027 interactions. Bioinformatics analysis showed that the interacting proteins reflect diverse functions, including roles in two-component system, transcription, protein degradation, and cell wall integrity. Functional investigations confirmed that PknG regulates cell wall integrity through key components of peptidoglycan (PG) biosynthesis, e.g. MurC. The global STPK-KPIs network constructed here is expected to serve as a rich resource for understanding the key signaling pathways in Mtb, thus facilitating drug development and effective control of Mtb.

Systematic Identification of Mycobacterium tuberculosis Effectors Reveals that BfrB Suppresses Innate Immunity.

Mycobacterium tuberculosis (Mtb) has evolved multiple strategies to counter the human immune system. The effectors of Mtb play important roles in the interactions with the host. However, because of the lack of highly efficient strategies, there are only a handful of known Mtb effectors, thus hampering our understanding of Mtb pathogenesis. In this study, we probed Mtb proteome microarray with biotinylated whole-cell lysates of human macrophages, identifying 26 Mtb membrane proteins and secreted proteins that bind to macrophage proteins. Combining GST pull-down with mass spectroscopy then enabled the specific identification of all binders. We refer to this proteome microarray-based strategy as SOPHIE (Systematic unlOcking of Pathogen and Host Interacting Effectors). Detailed investigation of a novel effector identified here, the iron storage protein BfrB (Rv3841), revealed that BfrB inhibits NF-κB-dependent transcription through binding and reducing the nuclear abundance of the ribosomal protein S3 (RPS3), which is a functional subunit of NF- κB. The importance of this interaction was evidenced by the promotion of survival in macrophages of the mycobacteria, Mycobacterium smegmatis, by overexpression of BfrB. Thus, beyond demonstrating the power of SOPHIE in the discovery of novel effectors of human pathogens, we expect that the set of Mtb effectors identified in this work will greatly facilitate the understanding of the pathogenesis of Mtb, possibly leading to additional potential molecular targets in the battle against tuberculosis.

A sub-milligram-synthesis protocol for in vitro screening of HDAC11 inhibitors.

This work demonstrated the high efficiency of a sub-milligram-synthesis based medicinal chemistry method. Totally 72 compounds, consisting a tri-substituted pyrrolidine core, were prepared. Around 0.1mg of each compound was solid-phase synthesized. Based on the additive property of UV absorptions of unconjugated chromophores of a molecule, these compounds were quantified by UV measurement. A hit, whose IC50 value was 1.2µM in HDAC11 inhibition assays, highlights the applicability of the approach reported here in future optimization works.

Differential regulation of the ten-eleven translocation (TET) family of dioxygenases by O-linked ß-N-acetylglucosamine transferase (OGT).

The ten-eleven translocation (TET) family of dioxygenases (TET1/2/3) converts 5-methylcytosine to 5-hydroxymethylcytosine and provides a vital mechanism for DNA demethylation. However, how TET proteins are regulated is largely unknown. Here we report that the O-linked ß-GlcNAc (O-GlcNAc) transferase (OGT) is not only a major TET3-interacting protein but also regulates TET3 subcellular localization and enzymatic activity. OGT catalyzes the O-GlcNAcylation of TET3, promotes TET3 nuclear export, and, consequently, inhibits the formation of 5-hydroxymethylcytosine catalyzed by TET3. Although TET1 and TET2 also interact with and can be O-GlcNAcylated by OGT, neither their subcellular localization nor their enzymatic activity are affected by OGT. Furthermore, we show that the nuclear localization and O-GlcNAcylation of TET3 are regulated by glucose metabolism. Our study reveals the differential regulation of TET family proteins by OGT and a novel link between glucose metabolism and DNA epigenetic modification.

RecJ-like protein from Pyrococcus furiosus has 3'-5' exonuclease activity on RNA: implications for proofreading of 3'-mismatched RNA primers in DNA replication.

Replicative DNA polymerases require an RNA primer for leading and lagging strand DNA synthesis, and primase is responsible for the de novo synthesis of this RNA primer. However, the archaeal primase from Pyrococcus furiosus (Pfu) frequently incorporates mismatched nucleoside monophosphate, which stops RNA synthesis. Pfu DNA polymerase (PolB) cannot elongate the resulting 3'-mismatched RNA primer because it cannot remove the 3'-mismatched ribonucleotide. This study demonstrates the potential role of a RecJ-like protein from P. furiosus (PfRecJ) in proofreading 3'-mismatched ribonucleotides. PfRecJ hydrolyzes single-stranded RNA and the RNA strand of RNA/DNA hybrids in the 3'-5' direction, and the kinetic parameters (Km and Kcat) of PfRecJ during RNA strand digestion are consistent with a role in proofreading 3'-mismatched RNA primers. Replication protein A, the single-stranded DNA-binding protein, stimulates the removal of 3'-mismatched ribonucleotides of the RNA strand in RNA/DNA hybrids, and Pfu DNA polymerase can extend the 3'-mismatched RNA primer after the 3'-mismatched ribonucleotide is removed by PfRecJ. Finally, we reconstituted the primer-proofreading reaction of a 3'-mismatched ribonucleotide RNA/DNA hybrid using PfRecJ, replication protein A, Proliferating cell nuclear antigen (PCNA) and PolB. Given that PfRecJ is associated with the GINS complex, a central nexus in archaeal DNA replication fork, we speculate that PfRecJ proofreads the RNA primer in vivo.

A rapid diagnostic technique based on metabolomics to differentiate between preeclampsia (PE) and chronic kidney disease (CKD) using maternal urine.

Similar clinical manifestations between preeclampsia and chronic kidney diseases can lead to potential misdiagnosis. Therefore, it is crucial to investigate effective diagnostic approaches that can reduce misdiagnosis and ensure the well-being of pregnant women. In this study, urine samples collected from 44 individuals with preeclampsia, 37 individuals with chronic kidney disease, and 37 healthy pregnant women were analyzed using metabolomic and proteomic strategies to distinguish between these two diseases. A total of 15 small molecules were tentatively identified as biomarkers to differentiate these two diseases, including potential internally exposed drugs and their metabolites like labetalol and SN-38, metabolites of exogenous substances like 3-phenylpropyl glucosinolate, and endogenous substances related to metabolism such as isoglobotriaose and chitobiose. Metabolic differences between preeclampsia from healthy pregnant women, as well as the differences between chronic kidney disease and healthy pregnant women were also investigated. Major mechanistic pathways were investigated based on the combination of metabolomic and proteomic, amino acid metabolisms and folate metabolism play key roles in distinguishing preeclampsia and chronic kidney disease. Two patients who were initially diagnosed with chronic kidney disease were found to have a closer association with preeclampsia following metabolomic analysis. Subsequent clinical symptoms and manifestations further supported the diagnosis of preeclampsia, and one of patient's pregnancy was ultimately terminated due to severe preeclampsia. Results of this study contribute to a better understanding of the pathogenesis and clinical diagnosis of preeclampsia, offering insights that could potentially improve future diagnostic and management approaches.

Integrative multi-omics analyses reveal vesicle transport as a potential target for thoracic aortic aneurysm.

BACKGROUND: Thoracic aortic aneurysm (TAA) refers to dilation and enlargement of the thoracic aorta caused by various reasons. Most patients have no apparent symptoms in the early stage and are subject to a poor prognosis once the aneurysm ruptures. It is crucial to identify individuals who are predisposed to TAA and to discover effective therapeutic targets for early intervention. METHODS: We conducted a label-free quantitative proteomic analysis among aorta tissue samples from TAA patients to screen differentially expressed proteins (DEPs) and key co-expression modules. Two datasets from Gene Expression Omnibus (GEO) database were included for integrative analysis, and the identified genes were subjected to immunohistochemistry (IHC) validation. Detailed vesicle transport related enrichment analysis was conducted and two FDA-approved drugs, chlorpromazine (CPZ) and chloroquine (CQ), were selected for in vivo inhibition of vesicle transport in mice TAA model. The diameter of thoracic aorta, mortality and histological differences after interventions were evaluated. RESULTS: We found significant enrichments in functions involved with vesicle transport, extracellular matrix organizing, and infection diseases in TAA. Endocytosis was the most essential vesicle transport process in TAA formation. Interventions with CPZ and CQ significantly reduced the aneurysm diameter and elastin degradation in vivo and enhanced the survival rates of TAA mice. CONCLUSIONS: We systematically screened the aberrantly regulated bioprocesses in TAA based on integrative multi-omics analyses, identified and demonstrated the importance of vesicle transport in the TAA formation. Our study provided pilot evidence that vesicular transport was a potential and promising target for the treatment of TAA.

Involvement of Ser94 in RNase HIII from Chlamydophila pneumoniae in the recognition of a single ribonucleotide misincorporated into double-stranded DNA.

We recently provided the first report that RNase HIII can cleave a DNA-rN(1)-DNA/DNA substrate (rN(1), one ribonucleotide) in vitro. In the present study, mutagenesis analyses and molecular dynamics (MD) simulations were performed on RNase HIII from Chlamydophila pneumoniae AR39 (CpRNase HIII). Our results elucidate the mechanism of ribonucleotide recognition employed by CpRNase HIII, indicating that the G95/K96/G97 motif of CpRNase HIII represents the main surface interacting with single ribonucleotides, in a manner similar to that of the GR(K)G motif of RNase HIIs. However, CpRNase HIII lacks the specific tyrosine required for RNase HII to recognize single ribonucleotides in double-stranded DNA (dsDNA). Interestingly, MD shows that Ser94 of CpRNase HIII forms a stable hydrogen bond with the deoxyribonucleotide at the (5')RNA-DNA(3') junction, moving this nucleotide away from the chimeric ribonucleotide. This movement appears to deform the nucleic acid backbone at the RNA-DNA junction and allows the ribonucleotide to interact with the GKG motif. Based on the inferences drawn from MD simulations, biochemical results indicated that Ser94 was necessary for catalytic activity on the DNA-rN(1)-DNA/DNA substrate; mutant S94V could bind this substrate but exhibited no cleavage. Mismatches opposite the single ribonucleotide misincorporated in dsDNA inhibited cleavage by CpRNase HIII to varying degrees but did not interfere with CpRNase/substrate binding. Further MD results implied that mismatches impair the interaction between Ser94 and the deoxyribonucleotide at the RNA-DNA junction. Consequently, recognition of the misincorporated ribonucleotide was disturbed. Our results may help elucidate the distinct substrate-recognition properties of different RNase Hs.

RNase HIII from Chlamydophila pneumoniae can efficiently cleave double-stranded DNA carrying a chimeric ribonucleotide in the presence of manganese.

Two ribonuclease Hs (RNase Hs) have been found in Chlamydophila pneumoniae, CpRNase HII and CpRNase HIII. This work is the first report that CpRNase HIII can efficiently cleave DNA-rN(1) -DNA/DNA (rN(1) , monoribonucleotide) in vitro in the presence of Mn(2+) , whereas the enzymatic activity of CpRNase HII on the same substrate was inhibited by Mn(2+) and dependent on Mg(2+) . However, the ability of both CpRNase Hs to cleave other alternative substrates (RNA/DNA hybrids and Okazaki-like substrates), was insensitive to the divalent ions changes, suggesting that high concentrations of Mn(2+) specifically repressed the ability of CpRNase HII to cleave DNA-rN(1) -DNA/DNA but activated this function in CpRNase HIII. Further in vivo experiments showed that the CpRNase HII complementation of Escherichia coli rnh(-) mutations in an Mg(2+) environment was suppressed by Mn(2+) . In contrast, Mn(2+) was indispensable for CpRNase HIII to complement the same mutations. Further, the cell growth inhibition and the genomic DNA sensitivity to alkali in the bacterial strain lacking RNase HII activity could be relieved by functional CpRNase HII or HIII with its compatible ion. Therefore, CpRNase HIII can execute cleavage activity on DNA-rN(1) -DNA/DNA under a Mn(2+) -rich environment and may function as a substitute for CpRNase HII under special physiological states.