Upregulation of RNA cap methyltransferase RNMT drives ribosome biogenesis during T cell activation.

The m7G cap is ubiquitous on RNAPII-transcribed RNA and has fundamental roles in eukaryotic gene expression, however its in vivo role in mammals has remained unknown. Here, we identified the m7G cap methyltransferase, RNMT, as a key mediator of T cell activation, which specifically regulates ribosome production. During T cell activation, induction of mRNA expression and ribosome biogenesis drives metabolic reprogramming, rapid proliferation and differentiation generating effector populations. We report that RNMT is induced by T cell receptor (TCR) stimulation and co-ordinates the mRNA, snoRNA and rRNA production required for ribosome biogenesis. Using transcriptomic and proteomic analyses, we demonstrate that RNMT selectively regulates the expression of terminal polypyrimidine tract (TOP) mRNAs, targets of the m7G-cap binding protein LARP1. The expression of LARP1 targets and snoRNAs involved in ribosome biogenesis is selectively compromised in Rnmt cKO CD4 T cells resulting in decreased ribosome synthesis, reduced translation rates and proliferation failure. By enhancing ribosome abundance, upregulation of RNMT co-ordinates mRNA capping and processing with increased translational capacity during T cell activation.

Genome-wide screens connect HD82 loss-of-function to purine analog resistance in African trypanosomes.

Nucleoside analogs have been used extensively as anti-infective agents, particularly against viral infections, and have long been considered promising anti-parasitic agents. These pro-drugs are metabolized by host-cell, viral, or parasite enzymes prior to incorporation into DNA, thereby inhibiting DNA replication. Here, we report genes that sensitize African trypanosomes to nucleoside analogs, including the guanosine analog, ganciclovir. We applied ganciclovir selective pressure to a trypanosome genome-wide knockdown library, which yielded nucleoside mono- and diphosphate kinases as hits, validating the approach. The two most dominant hits to emerge, however, were Tb927.6.2800 and Tb927.6.2900, which both encode nuclear proteins; the latter of which is HD82, a SAMHD1-related protein and a putative dNTP triphosphohydrolase. We independently confirmed that HD82, which is conserved among the trypanosomatids, can sensitize Trypanosoma brucei to ganciclovir. Since ganciclovir activity depends upon phosphorylation by ectopically expressed viral thymidine kinase, we also tested the adenosine analog, ara-A, that may be fully phosphorylated by native T. brucei kinase(s). Both Tb927.6.2800 and HD82 knockdowns were resistant to this analog. Tb927.6.2800 knockdown increased sensitivity to hydroxyurea, while dNTP analysis indicated that HD82 is indeed a triphosphohydrolase with dATP as the preferred substrate. Our results provide insights into nucleoside/nucleotide metabolism and nucleoside analog metabolism and resistance in trypanosomatids. We suggest that the product of 6.2800 sensitizes cells to purine analogs through DNA repair, while HD82 does so by reducing the native purine pool.IMPORTANCEThere is substantial interest in developing nucleoside analogs as anti-parasitic agents. We used genome-scale genetic screening and discovered two proteins linked to purine analog resistance in African trypanosomes. Our screens also identified two nucleoside kinases required for pro-drug activation, further validating the approach. The top novel hit, HD82, is related to SAMHD1, a mammalian nuclear viral restriction factor. We validated HD82 and localized the protein to the trypanosome nucleus. HD82 appears to sensitize trypanosomes to nucleoside analogs by reducing native pools of nucleotides, providing insights into both nucleoside/nucleotide metabolism and nucleoside analog resistance in trypanosomatids.

DIA label-free proteomic analysis of murine bone-marrow-derived macrophages.

Here, we describe an optimized protocol to analyze murine bone-marrow-derived macrophages using label-free data-independent acquisition (DIA) proteomics. We provide a complete step-by-step protocol describing sample preparation utilizing the S-Trap approach for on-column digestion and peptide purification. We then detail mass spectrometry data acquisition and approaches for data analysis. Single-shot DIA protocols achieve comparable proteomic depth with data-dependent MS approaches without the need for fractionation. This allows for better scaling for large sample numbers with high inter-experimental reproducibility. For complete details on the use and execution of this protocol, please refer to Ryan et al. (2022).

SMN Depleted Mice Offer a Robust and Rapid Onset Model of Nonalcoholic Fatty Liver Disease.

BACKGROUND & AIMS: Nonalcoholic fatty liver disease (NAFLD) is considered a health epidemic with potential devastating effects on the patients and the healthcare systems. Current preclinical models of NAFLD are invariably imperfect and generally take a long time to develop. A mouse model of survival motor neuron (SMN) depletion (Smn2B/- mice) was recently shown to develop significant hepatic steatosis in less than 2 weeks from birth. The rapid onset of fatty liver in Smn2B/- mice provides an opportunity to identify molecular markers of NAFLD. Here, we investigated whether Smn2B/- mice display typical features of NAFLD/nonalcoholic steatohepatitis (NASH). METHODS: Biochemical, histologic, electron microscopy, proteomic, and high-resolution respirometry were used. RESULTS: The Smn2B/- mice develop microvesicular steatohepatitis within 2 weeks, a feature prevented by AAV9-SMN gene therapy. Although fibrosis is not overtly apparent in histologic sections of the liver, there is molecular evidence of fibrogenesis and presence of stellate cell activation. The consequent liver damage arises from mitochondrial reactive oxygen species production and results in hepatic dysfunction in protein output, complement, coagulation, iron homeostasis, and insulin-like growth factor-1 metabolism. The NAFLD phenotype is likely due to non-esterified fatty acid overload from peripheral lipolysis subsequent to hyperglucagonemia compounded by reduced muscle use and insulin resistance. Despite the low hepatic mitochondrial content, isolated mitochondria show enhanced ß-oxidation, likely as a compensatory response, resulting in the production of reactive oxygen species. In contrast to typical NAFLD/NASH, the Smn2B/- mice lose weight because of their associated neurological condition (spinal muscular atrophy) and develop hypoglycemia. CONCLUSIONS: The Smn2B/- mice represent a good model of microvesicular steatohepatitis. Like other models, it is not representative of the complete NAFLD/NASH spectrum. Nevertheless, it offers a reliable, low-cost, early-onset model that is not dependent on diet to identify molecular players in NAFLD pathogenesis and can serve as one of the very few models of microvesicular steatohepatitis for both adult and pediatric populations.

Stoichiometric quantification of Akt phosphorylation using LC-MS/MS.

The Ptdlns-3-kinase (PI3-K) signaling pathway plays a vital role in cell survival, proliferation, apoptosis and differentiation in normal cells, as well as in diseases such as cancer and diabetes. Quantification of phospho-Akt is a standard way of assessing the activity of the PI3-K signaling pathway in both cells and tumors. This measurement is traditionally performed semiquantitatively using immunoassays such as Western blot. Here we report an LC-MS method to accurately measure the stoichiometry of Akt phosphorylation in biological samples. The procedure includes immunoprecipitation, gel electrophoresis, in-gel digestion, addition of isotopicaly labeled internal standards and LC-MS/MS. Two proteolytic enzymes, chymotrypsin and trypsin, were used to generate suitable peptide fragments for measuring Thr308 and Ser473 phosphorylation, respectively. The interday imprecision was estimated to be 3.8% and 2.3% for Thr308 and Ser473, respectively. This method has been tested on human T-cells grown in presence and absence of pervanadate and with or without a PI3-K inhibitor and on human glioblastoma cells (U-87 MG) grown in presence and absence of wortmannin (PI3-K inhibitor).The results of T cells suggest that the levels of Akt phosphorylation in untreated cells were below 1% for both phosphorylation sites. Pervanadate treatment provoked an 18-fold increase in phosphorylation of Thr308 and the PI3-K inhibitor partially reversed the increase. A comparison between LC-MS/MS and Western blotting suggests that the LC-MS based method is of comparable sensitivity and provides a more accurate phosphorylation stoichiometry, a wider dynamic range and more in-depth information. The application of the new method and its utility to providing predictive markers of response to targeted therapies is discussed.

CAP-MAP: cap analysis protocol with minimal analyte processing, a rapid and sensitive approach to analysing mRNA cap structures.

Eukaryotic messenger RNA (mRNA) is modified by the addition of an inverted guanosine cap to the 5' triphosphate. The cap guanosine and initial transcribed nucleotides are further methylated by a series of cap methyltransferases to generate the mature cap structures which protect RNA from degradation and recruit proteins involved in RNA processing and translation. Research demonstrating that the cap methyltransferases are regulated has generated interest in determining the methylation status of the mRNA cap structures present in cells. Here, we present CAP-MAP: cap analysis protocol with minimal analyte processing, a rapid and sensitive method for detecting cap structures present in mRNA isolated from tissues or cultured cells.

Mechanism of Activation of AMPK by Cordycepin.

Cordycepin (3'-deoxyadenosine) is a major bioactive agent in Cordyceps militaris, a fungus used in traditional Chinese medicine. It has been proposed to have many beneficial metabolic effects by activating AMP-activated protein kinase (AMPK), but the mechanism of activation remained uncertain. We report that cordycepin enters cells via adenosine transporters and is converted by cellular metabolism into mono-, di-, and triphosphates, which at high cordycepin concentrations can almost replace cellular adenine nucleotides. AMPK activation by cordycepin in intact cells correlates with the content of cordycepin monophosphate and not other cordycepin or adenine nucleotides. Genetic knockout of AMPK sensitizes cells to the cytotoxic effects of cordycepin. In cell-free assays, cordycepin monophosphate mimics all three effects of AMP on AMPK, while activation in cells is blocked by a γ-subunit mutation that prevents activation by AMP. Thus, cordycepin is a pro-drug that activates AMPK by being converted by cellular metabolism into the AMP analog cordycepin monophosphate.

Phenformin, But Not Metformin, Delays Development of T Cell Acute Lymphoblastic Leukemia/Lymphoma via Cell-Autonomous AMPK Activation.

AMPK acts downstream of the tumor suppressor LKB1, yet its role in cancer has been controversial. AMPK is activated by biguanides, such as metformin and phenformin, and metformin use in diabetics has been associated with reduced cancer risk. However, whether this is mediated by cell-autonomous AMPK activation within tumor progenitor cells has been unclear. We report that T-cell-specific loss of AMPK-α1 caused accelerated growth of T cell acute lymphoblastic leukemia/lymphoma (T-ALL) induced by PTEN loss in thymic T cell progenitors. Oral administration of phenformin, but not metformin, delayed onset and growth of lymphomas, but only when T cells expressed AMPK-α1. This differential effect of biguanides correlated with detection of phenformin, but not metformin, in thymus. Phenformin also enhanced apoptosis in T-ALL cells both in vivo and in vitro. Thus, AMPK-α1 can be a cell-autonomous tumor suppressor in the context of T-ALL, and phenformin may have potential for the prevention of some cancers.

Mechanisms of Paradoxical Activation of AMPK by the Kinase Inhibitors SU6656 and Sorafenib.

SU6656, a Src kinase inhibitor, was reported to increase fat oxidation and reduce body weight in mice, with proposed mechanisms involving AMP-activated protein kinase (AMPK) activation via inhibition of phosphorylation of either LKB1 or AMPK by the Src kinase, Fyn. However, we report that AMPK activation by SU6656 is independent of Src kinases or tyrosine phosphorylation of LKB1 or AMPK and is not due to decreased cellular energy status or binding at the ADaM site on AMPK. SU6656 is a potent AMPK inhibitor, yet binding at the catalytic site paradoxically promotes phosphorylation of Thr172 by LKB1. This would enhance phosphorylation of downstream targets provided the lifetime of Thr172 phosphorylation was sufficient to allow dissociation of the inhibitor and subsequent catalysis prior to its dephosphorylation. By contrast, sorafenib, a kinase inhibitor in clinical use, activates AMPK indirectly by inhibiting mitochondrial metabolism and increasing cellular AMP:ADP and/or ADP:ATP ratios.

Proteomic profiling of neuronal mitochondria reveals modulators of synaptic architecture.

BACKGROUND: Neurons are highly polarized cells consisting of three distinct functional domains: the cell body (and associated dendrites), the axon and the synapse. Previously, it was believed that the clinical phenotypes of neurodegenerative diseases were caused by the loss of entire neurons, however it has recently become apparent that these neuronal sub-compartments can degenerate independently, with synapses being particularly vulnerable to a broad range of stimuli. Whilst the properties governing the differential degenerative mechanisms remain unknown, mitochondria consistently appear in the literature, suggesting these somewhat promiscuous organelles may play a role in affecting synaptic stability. Synaptic and non-synaptic mitochondrial subpools are known to have different enzymatic properties (first demonstrated by Lai et al., 1977). However, the molecular basis underpinning these alterations, and their effects on morphology, has not been well documented. METHODS: The current study has employed electron microscopy, label-free proteomics and in silico analyses to characterize the morphological and biochemical properties of discrete sub-populations of mitochondria. The physiological relevance of these findings was confirmed in-vivo using a molecular genetic approach at the Drosophila neuromuscular junction. RESULTS: Here, we demonstrate that mitochondria at the synaptic terminal are indeed morphologically different to non-synaptic mitochondria, in both rodents and human patients. Furthermore, generation of proteomic profiles reveals distinct molecular fingerprints - highlighting that the properties of complex I may represent an important specialisation of synaptic mitochondria. Evidence also suggests that at least 30% of the mitochondrial enzymatic activity differences previously reported can be accounted for by protein abundance. Finally, we demonstrate that the molecular differences between discrete mitochondrial sub-populations are capable of selectively influencing synaptic morphology in-vivo. We offer several novel mitochondrial candidates that have the propensity to significantly alter the synaptic architecture in-vivo. CONCLUSIONS: Our study demonstrates discrete proteomic profiles exist dependent upon mitochondrial subcellular localization and selective alteration of intrinsic mitochondrial proteins alters synaptic morphology in-vivo.

IFI16 and cGAS cooperate in the activation of STING during DNA sensing in human keratinocytes.

Many human cells can sense the presence of exogenous DNA during infection though the cytosolic DNA receptor cyclic GMP-AMP synthase (cGAS), which produces the second messenger cyclic GMP-AMP (cGAMP). Other putative DNA receptors have been described, but whether their functions are redundant, tissue-specific or integrated in the cGAS-cGAMP pathway is unclear. Here we show that interferon-γ inducible protein 16 (IFI16) cooperates with cGAS during DNA sensing in human keratinocytes, as both cGAS and IFI16 are required for the full activation of an innate immune response to exogenous DNA and DNA viruses. IFI16 is also required for the cGAMP-induced activation of STING, and interacts with STING to promote STING phosphorylation and translocation. We propose that the two DNA sensors IFI16 and cGAS cooperate to prevent the spurious activation of the type I interferon response.

Outer chain N-glycans are required for cell wall integrity and virulence of Candida albicans.

The outer layer of the Candida albicans cell wall is enriched in highly glycosylated mannoproteins that are the immediate point of contact with the host and strongly influence the host-fungal interaction. N-Glycans are the major form of mannoprotein modification and consist of a core structure, common to all eukaryotes, that is further elaborated in the Golgi to form the highly branched outer chain that is characteristic of fungi. In yeasts, outer chain branching is initiated by the action of the alpha1,6-mannosyltransferase Och1p; therefore, we disrupted the C. albicans OCH1 homolog to determine the importance of outer chain N-glycans on the host-fungal interaction. Loss of CaOCH1 resulted in a temperature-sensitive growth defect and cellular aggregation. Outer chain elongation of N-glycans was absent in the null mutant, demonstrated by the lack of the alpha1,6-linked polymannose backbone and the underglycosylation of N-acetylglucosaminidase. A null mutant lacking OCH1 was hypersensitive to a range of cell wall perturbing agents and had a constitutively activated cell wall integrity pathway. These mutants had near normal growth rates in vitro but were attenuated in virulence in a murine model of systemic infection. However, tissue burdens for the Caoch1delta null mutant were similar to control strains with normal N-glycosylation, suggesting the host-fungal interaction was altered such that high burdens were tolerated. This demonstrates the importance of N-glycan outer chain epitopes to the host-fungal interaction and virulence.

Trypanosoma brucei glycoproteins contain novel giant poly-N-acetyllactosamine carbohydrate chains.

The flagellar pocket of the bloodstream form of the African sleeping sickness parasite Trypanosoma brucei contains material that binds the beta-d-galactose-specific lectin ricin (Brickman, M. J., and Balber, A. E. (1990) J. Protozool. 37, 219-224). Glycoproteins were solubilized from bloodstream form T. brucei cells in 8 M urea and 3% SDS and purified by ricin affinity chromatography. Essentially all binding of ricin to these glycoproteins was abrogated by treatment with peptide N-glycosidase, showing that the ricin ligands are attached to glycoproteins via N-glycosidic linkages to asparagine residues. Glycans released by peptide N-glycosidase were resolved by Bio-Gel P-4 gel filtration into two fractions: a low molecular mass mannose-rich fraction and a high molecular mass galactose and N-acetylglucosamine-rich fraction. The latter fraction was further separated by high pH anion exchange chromatography and analyzed by gas chromatography mass spectrometry, one- and two-dimensional NMR, electrospray mass spectrometry, and methylation linkage analysis. The high molecular mass ricin-binding N-glycans are based on a conventional Manalpha1-3(Manalpha1-6)Manbeta1-4-GlcNAcbeta1-4GlcNAc core structure and contain poly-N-acetyllactosamine chains. A significant proportion of these structures are extremely large and of unusual structure. They contain an average of 54 N-acetyllactosamine (Galbeta1-4GlcNAc) repeats per glycan, linked mostly by -4GlcNAcbeta1-6Galbeta1-interrepeat linkages, with an average of one -4GlcNAcbeta1-3(-4GlcNAcbeta1-6)Galbeta1- branch point in every six repeats. These structures, which also bind tomato lectin, are twice the size reported for the largest mammalian poly-N-acetyllactosamine N-linked glycans and also differ in their preponderance of -4GlcNAcbeta1-6Galbeta1- over -4GlcNacbeta1-3Galbeta1- interrepeat linkages. Molecular modeling suggests that -4GlcNAcbeta1-6Galbeta1- interrepeat linkages produce relatively compact structures that may give these giant N-linked glycans unique physicochemical properties. Fluorescence microscopy using fluorescein isothiocyanatericin indicates that ricin ligands are located mainly in the flagellar pocket and in the endosomal/lysosomal system of the trypanosome.

Characterization of LytH, a differentiation-associated peptidoglycan hydrolase of Bacillus subtilis involved in endospore cortex maturation.

The cortex peptidoglycan from endospores of Bacillus subtilis is responsible for the maintenance of dormancy. LytH (YunA) has been identified as a novel sporulation-specific component with a role in cortex structure determination. The lytH gene was expressed only during sporulation, under the control of the mother cell-specific sigma factor sigma(K). Spores of a lytH mutant have slightly reduced heat resistance and altered staining when viewed by electron microscopy. Analysis of the peptidoglycan structure of lytH mutant spores shows the loss of muramic acid residues substituted with L-alanine and a corresponding increase in muramic acid residues substituted with tetrapeptide compared to those in the parent strain. In a lytH cwlD mutant, the lack of muramic acid residues substituted with L-alanine and delta-lactam leaves 97% of residues substituted with tetrapeptide. These results suggest that lytH encodes an L-Ala-D-Glu peptidase involved in production of single L-alanine side chains from tetrapeptides in the spore cortex. The lack of di- or tripeptides in a lytH mutant reveals the enzyme is an endopeptidase.

LytG of Bacillus subtilis is a novel peptidoglycan hydrolase: the major active glucosaminidase.

LytG (YubE) of Bacillus subtilis is a novel 32 kDa autolysin produced during vegetative growth under the control of Esigma(A) RNA polymerase. Muropeptide analysis of vegetative cells of B. subtilis revealed LytG to be the major glucosaminidase responsible for peptidoglycan structural determination during vegetative growth. Overexpression and purification of LytG allowed its biochemical characterization. Despite sequence homology suggesting muramidase activity, LytG is a novel glucosaminidase with exoenzyme activity and may form part of a novel family of autolysins. It is involved in cell division, lysis, and motility on swarm plates.

A polysaccharide deacetylase gene (pdaA) is required for germination and for production of muramic delta-lactam residues in the spore cortex of Bacillus subtilis.

The predicted amino acid sequence of Bacillus subtilis yfjS (renamed pdaA) exhibits high similarity to those of several polysaccharide deacetylases. Beta-galactosidase fusion experiments and results of Northern hybridization with sporulation sigma mutants indicated that the pdaA gene is transcribed by E(sigma)(G) RNA polymerase. pdaA-deficient spores were bright by phase-contrast microscopy, and the spores were induced to germination on the addition of L-alanine. Germination-associated spore darkening, a slow and partial decrease in absorbance, and slightly lower dipicolinic acid release compared with that by the wild-type strain were observed. In particular, the release of hexosamine-containing materials was lacking in the pdaA mutant. Muropeptide analysis indicated that the pdaA-deficient spores completely lacked muramic delta-lactam. A pdaA-gfp fusion protein constructed in strain 168 and pdaA-deficient strains indicated that the protein is localized in B. subtilis spores. The biosynthetic pathway of muramic delta-lactam is discussed.

Analysis of spore cortex lytic enzymes and related proteins in Bacillus subtilis endospore germination.

The location and function of recognized cortex-lytic enzymes of Bacillus subtilis have been explored, and the involvement in germination of a number of related proteins tested. The SleB and CwlJ proteins are cortex-lytic enzymes, partially redundant in function, that are required together for effective cortex hydrolysis during B. subtilis spore germination. Spores were fractionated, and Western blotting of individual fractions suggests that the CwlJ protein is localized exclusively to the outer layers, or integument. The second spore-lytic enzyme, SleB, is localized both in the inner membrane of the spore and in the integument fraction. Neither protein changes location or size as the spore germinates. The ypeB gene is the second gene in a bicistronic operon with sleB. The SleB protein is absent from ypeB mutant spores, suggesting that YpeB is required for its localization or stabilization. In fractions of wild-type spores, the YpeB protein is found in the same locations as SleB - in both the inner membrane and the integument. As the absence of CwlJ protein does not affect the overall RP-HPLC profile of peptidoglycan fragments in germinating spores, this enzyme's hydrolytic specificity could not be defined. The effects of inactivation of several homologues of cortex-lytic enzymes of as yet undefined function were examined, by testing null mutants for their germination behaviour by OD(600) fall and by RP-HPLC of peptidoglycan fragments from dormant and germinating spores. The YaaH enzyme is responsible for a likely epimerase modification of peptidoglycan during spore germination, but the loss of this activity does not appear to affect the spore's ability to complete germination. Unlike the other cortex-lytic enzymes, the YaaH protein is present in large amounts in the spore germination exudate of B. subtilis. Mutants lacking either YdhD or YvbX, both homologues of YaaH, had no detectable alteration in either dormant or germinating spore peptidoglycan, and germinated normally. The ykvT gene, which encodes a protein of the SleB/CwlJ family, has no apparent association with germination: the gene is expressed in vegetative cells, and mutants lacking YkvT have no detectable phenotype.

Structural analysis of Bacillus megaterium KM spore peptidoglycan and its dynamics during germination.

The composition and structure of peptidoglycan from dormant spores of Bacillus megaterium KM and its dynamics during germination were investigated. Amino acid analysis and mass spectrometry identified 21 muropeptides resolved by reverse phase HPLC following digestion of peptidoglycan with Cellosyl. The basic structure of peptidoglycan in B. megaterium spores is similar to that of Bacillus subtilis: 44.2% of muramic acid residues are substituted with delta-lactam, 28.8% with single L-alanine, 25.1% with tetrapeptide and only 1.8% with tripeptide. The cross-linking index of the spore peptidoglycan, determined from muropeptides resolved by reverse phase HPLC, was 2.2 % per muramic acid. Spore peptidoglycan contains 2.9% of muropeptides with unsubstituted N-acetylmuramic acid. These muropeptides are likely to be intermediate products of delta-lactam formation. Analysis of muropeptide dynamics during germination revealed the activity of at least two hydrolytic enzymes, an N-acetylglucosaminidase and a lytic transglycosylase. A 4 M LiCl extract from 30 min germinated spores of B. megaterium KM caused 'germination-like' changes to permeabilized spores of B. megaterium and B. subtilis but not those of a B. subtilis cwlD mutant. Muropeptide analysis of the treated spores revealed the presence of products generated by the activity of a glucosaminidase.

Complete spore-cortex hydrolysis during germination of Bacillus subtilis 168 requires SleB and YpeB.

The role of the sleB gene of Bacillus subtilis, which encodes a putative spore-cortex-lytic enzyme, and the downstream ypeB gene were investigated. Both SleB and YpeB were required for normal germination to occur. The corresponding mutants formed phase-bright, heat-resistant spores with no apparent defects in dormancy. However, mutant spore suspensions lost optical density slower than the wild-type and spores were phase-grey even 12 h after the triggering of germination. Since the loss of heat resistance and release of dipicolinic acid was similar to the wild-type, these mutants were blocked in the later stages of germination. The mutants were nevertheless capable of outgrowth on rich agar to form colonies, indicating that other spore components can compensate for their function sufficiently to allow outgrowth. The expression and regulation of the operon was examined using a lacZ transcriptional fusion. Expression of the operon began 2 h after the onset of sporulation and was under the control of RNA polymerase containing the forespore-specific sigma factor, sigmaG. The application of reverse phase HPLC revealed that the mutants do not have any structural defect in the dormant spore cortex and therefore these genes are not required for normal spore-cortex synthesis. The analysis of peptidoglycan dynamics during germination showed, however, that the cortex was only partially hydrolysed in both mutants. This analysis also revealed that the likely hydrolytic bond specificity of SleB is likely to be that of a lytic transglycosylase.