Association of NOD2 leucine-rich repeat variants with susceptibility to Crohn's disease

Crohn's disease and ulcerative colitis, the two main types of chronic inflammatory bowel disease, are multifactorial conditions of unknown aetiology. A susceptibility locus for Crohn's disease has been mapped to chromosome 16. Here we have used a positional-cloning strategy, based on linkage analysis followed by linkage disequilibrium mapping, to identify three independent associations for Crohn's disease: a frameshift variant and two missense variants of NOD2, encoding a member of the Apaf-1/Ced-4 superfamily of apoptosis regulators that is expressed in monocytes. These NOD2 variants alter the structure of either the leucine-rich repeat domain of the protein or the adjacent region. NOD2 activates nuclear factor NF-kB; this activating function is regulated by the carboxy-terminal leucine-rich repeat domain, which has an inhibitory role and also acts as an intracellular receptor for components of microbial pathogens. These observations suggest that the NOD2 gene product confers susceptibility to Crohn's disease by altering the recognition of these components and/or by over-activating NF-kB in monocytes, thus documenting a molecular model for the pathogenic mechanism of Crohn's disease that can now be further investigated.

Identification of a chromosome 18q gene that is altered in colorectal cancers

Allelic deletions involving chromosome 18q occur in more than 70 percent of colorectal cancers. Such deletions are thought to signal the existence of a tumor suppressor gene in the affected region, but until now a candidate suppressor gene on this chromosomal arm had not been identified. A contiguous stretch of DNA comprising 370 kilobase pairs (kb) has now been cloned from a region of chromosome 18q suspected to reside near this gene. Potential exons in the 370-kb region were defined by human-rodent sequence identities, and the expression of potential exons was assessed by an "exon-connection" strategy based on the polymerase chain reaction. Expressed exons were used as probes for cDNA screening to obtain clones that encoded a portion of a gene termed DCC; this cDNA was encoded by at least eight exons within the 370-kb genomic region. The predicted amino acid sequence of the cDNA specified a protein with sequence similarity to neural cell adhesion molecules and other related cell surface glycoproteins. While the DCC gene was expressed in most normal tissues, including colonic mucosa, its expression was greatly reduced or absent in most colorectal carcinomas tested. Somatic mutations within the DCC gene observed in colorectal cancers included a homozygous deletion of the 5' end of the gene, a point mutation within one of the introns, and ten examples of DNA insertions within a 0.17-kb fragment immediately downstream of one of the exons. The DCC gene may play a role in the pathogenesis of human colorectal neoplasia, perhaps through alteration of the normal cell-cell interactions controlling growth.

Enhanced sensitivity of PTEN-deficient tumors to inhibition of FRAP/mTOR

Recent evidence places the FRAP/mTOR kinase downstream of the phosphatidyl inositol 3-kinase/Akt-signaling pathway, which is up-regulated in multiple cancers because of loss of the PTEN tumor suppressor gene. We performed biological and biochemical studies to determine whether PTEN-deficient cancer cells are sensitive to pharmacologic inhibition of FRAP/mTOR by using the rapamycin derivative CCI-779. In vitro and in vivo studies of isogenic PTEN(+/+) and PTEN(-/-) mouse cells as well as human cancer cells with defined PTEN status showed that the growth of PTEN null cells was blocked preferentially by pharmacologic FRAP/mTOR inhibition. Enhanced tumor growth caused by constitutive activation of Akt in PTEN(+/+) cells also was reversed by CCI-779 treatment, indicating that FRAP/mTOR functions downstream of Akt in tumorigenesis. Loss of PTEN correlated with increased S6 kinase activity and phosphorylation of ribosomal S6 protein, providing evidence for activation of the FRAP/mTOR pathway in these cells. Differential sensitivity to CCI-779 was not explained by differences in biochemical blockade of the FRAP/mTOR pathway, because S6 phosphorylation was inhibited in sensitive and resistant cell lines. These results provide rationale for testing FRAP/mTOR inhibitors in PTEN null human cancers.

Novel dihydropyridines with positive inotropic action through activation of Ca2+ channels

Transmembrane influx of extracellular calcium through specific calcium channels is now accepted to have an important role in the excitation-contraction coupling of cardiac and smooth muscle. The importance of such slow calcium channels has been underlined by the development of specific calcium channel blocking agents, the 'calcium antagonists', typified by verapamil, nifedipine and diltiazem. These drugs have been used to investigate the properties of slow calcium channels in a variety of tissues. We have found that small modifications to the nifedipine molecule produce other dihydropyridine derivatives (see Fig. 1) with effects diametrically opposite to those of the calcium antagonists: cardiac contractility is stimulated and smooth muscle is contracted. These effects are competitively antagonized by nifedipine. Apparently, nifedipine and the novel compounds bind to the same specific dihydropyridine binding sites in or near the calcium channel. In contrast to nifedipine, however, the new compounds promote--instead of inhibiting--the influx of Ca2+ ions. We report here the properties of BAY K 8644 (methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)- pyridine-5-carboxylate), one of the most potent of these novel compounds.

Rapamycin suppresses 5'TOP mRNA translation through inhibition of p70s6k

Treatment of mammalian cells with the immunosuppressant rapamycin, a bacterial macrolide, selectively suppresses mitogen-induced translation of an essential class of mRNAs which contain an oligopyrimidine tract at their transcriptional start (5'TOP), most notably mRNAs encoding ribosomal proteins and elongation factors. In parallel, rapamycin blocks mitogen-induced p70 ribosomal protein S6 kinase (p70s6k) phosphorylation and activation. Utilizing chimeric mRNA constructs containing either a wild-type or disrupted 5'TOP, we demonstrate that an intact polypyrimidine tract is required for rapamycin to elicit an inhibitory effect on the translation of these transcripts. In turn, a dominant-interfering p70s6k, which selectively prevents p70s6k activation by blocking phosphorylation of the rapamycin-sensitive sites, suppresses the translation of the chimeric mRNA containing the wild-type but not the disrupted 5'TOP. Conversion of the principal rapamycin-sensitive p70s6k phosphorylation site, T389, to an acidic residue confers rapamycin resistance on the kinase and negates the inhibitory effects of the macrolide on 5'TOP mRNA translation in cells expressing this mutant. The results demonstrate that the rapamycin block of mitogen-induced 5'TOP mRNA translation is mediated through inhibition of p70s6k activation.

Mammalian TOR: a homeostatic ATP sensor

The bacterial macrolide rapamycin is an efficacious anticancer agent against solid tumors. In a hypoxic environment, the increase in mass of solid tumors is dependent on the recruitment of mitogens and nutrients. When nutrient concentrations change, particularly those of essential amino acids, the mammalian Target of Rapamycin (mTOR) functions in regulatory pathways that control ribosome biogenesis and cell growth. In bacteria, ribosome biogenesis is independently regulated by amino acids and adenosine triphosphate (ATP). Here we demonstrate that the mTOR pathway is influenced by the intracellular concentration of ATP, independent of the abundance of amino acids, and that mTOR itself is an ATP sensor.

Mapping of a susceptibility locus for Crohn's disease on chromosome 16

Crohn's disease (CD) and ulcerative colitis are the major forms of chronic inflammatory bowel diseases in the western world, and occur in young adults with an estimated prevalence of more than one per thousand inhabitants. The causes of inflammatory bowel diseases remain unknown, but genetic epidemiology studies suggest that inherited factors may contribute in part to variation in individual susceptibility to Crohn's disease. A genome-wide search performed on two consecutive and independent panels of families with multiple affected members, using a non-parametric two-point sibling-pair linkage method, identified a putative CD-susceptibility locus on chromosome 16 (P less than 0.01 for each panel). The localization was centered around loci D16S409 and D16S419 by using multipoint sibpair analysis (P less than 1.5x10(-5)). This region of the genome contains candidate genes which may be relevant to the pathogenic mechanism of inflammatory bowel diseases.

CARD15 mutations in Blau syndrome

We have identified three missense mutations in the nucleotide-binding domain (NBD) of CARD15/NOD2 in four French and German families with Blau syndrome. Our findings indicate that, in addition to Crohn disease, CARD15 is involved in the susceptibility to a second granulomatous disorder.

Phosphorylation and activation of p70s6k by PDK1

Activation of the protein p70s6k by mitogens leads to increased translation of a family of messenger RNAs that encode essential components of the protein synthetic apparatus. Activation of the kinase requires hierarchical phosphorylation at multiple sites, culminating in the phosphorylation of the threonine in position 229 (Thr229), in the catalytic domain. The homologous site in protein kinase B (PKB), Thr308, has been shown to be phosphorylated by the phosphoinositide-dependent protein kinase PDK1. A regulatory link between p70s6k and PKB was demonstrated, as PDK1 was found to selectively phosphorylate p70s6k at Thr229. More importantly, PDK1 activated p70s6k in vitro and in vivo, whereas the catalytically inactive PDK1 blocked insulin-induced activation of p70s6k.

Drosophila S6 kinase: a regulator of cell size

Cell proliferation requires cell growth; that is, cells only divide after they reach a critical size. However, the mechanisms by which cells grow and maintain their appropriate size have remained elusive. Drosophila deficient in the S6 kinase gene (dS6K) exhibited an extreme delay in development and a severe reduction in body size. These flies had smaller cells rather than fewer cells. The effect was cell-autonomous, displayed throughout larval development, and distinct from that of ribosomal protein mutants (Minutes). Thus, the dS6K gene product regulates cell size in a cell-autonomous manner without impinging on cell number.

Identification of an anti-inflammatory protein from Faecalibacterium prausnitzii, a commensal bacterium deficient in Crohn's disease

BACKGROUND

Crohn's disease (CD)-associated dysbiosis is characterised by a loss of Faecalibacterium prausnitzii, whose culture supernatant exerts an anti-inflammatory effect both in vitro and in vivo. However, the chemical nature of the anti-inflammatory compounds has not yet been determined.

METHODS

Peptidomic analysis using mass spectrometry was applied to F. prausnitzii supernatant. Anti-inflammatory effects of identified peptides were tested in vitro directly on intestinal epithelial cell lines and on cell lines transfected with a plasmid construction coding for the candidate protein encompassing these peptides. In vivo, the cDNA of the candidate protein was delivered to the gut by recombinant lactic acid bacteria to prevent dinitrobenzene sulfonic acid (DNBS)-colitis in mice.

RESULTS

The seven peptides, identified in the F. prausnitzii culture supernatants, derived from a single microbial anti-inflammatory molecule (MAM), a protein of 15 kDa, and comprising 53% of non-polar residues. This last feature prevented the direct characterisation of the putative anti-inflammatory activity of MAM-derived peptides. Transfection of MAM cDNA in epithelial cells led to a significant decrease in the activation of the nuclear factor (NF)-κB pathway with a dose-dependent effect. Finally, the use of a food-grade bacterium, Lactococcus lactis, delivering a plasmid encoding MAM was able to alleviate DNBS-induced colitis in mice.

CONCLUSIONS

A 15 kDa protein with anti-inflammatory properties is produced by F. prausnitzii, a commensal bacterium involved in CD pathogenesis. This protein is able to inhibit the NF-κB pathway in intestinal epithelial cells and to prevent colitis in an animal model.

Ribosomal S6 kinase signaling and the control of translation

The highly homologous 40S ribosomal protein S6 kinases (S6K1 and S6K2) play a key role in the regulation of cell growth by controlling the biosynthesis of translational components which make up the protein synthetic apparatus, most notably ribosomal proteins. In the case of S6K1, at least eight phosphorylation sites are believed to mediate kinase activation in a hierarchical fashion. Activation is initiated by phosphatidylinositide-3OH kinase (PI3K)-mediated phosphorylation of key residues in the carboxy-terminus of the kinase, allowing phosphorylation of a critical residue residing in the activation loop of the catalytic domain by phosphoinositide-dependent kinase 1 (PDK1). The kinases responsible for phosphorylating the carboxy-terminal sites have yet to be identified. Additionally, S6 kinases are under the control of the PI3K relative, mammalian Target Of Rapamycin (mTOR), which may serve an additional function as a checkpoint for amino acid availability. In this review we set out to discuss the present state of knowledge regarding upstream signaling components which have been implicated in the control of S6K1 activation and the role of the kinase in controlling cell growth through regulating ribosome biogenesis at the translational level.

beta-Amyloid-mediated vasoactivity and vascular endothelial damage

Deposits of beta-amyloid are apparent in ageing and Alzheimer's disease, but the role of this peptide in neurodegeneration is unclear. The free-radical theory of ageing may also account for Alzheimer-type degeneration and consequently links between free-radical generation and beta-amyloid have been sought. We demonstrate here that beta-amyloid interacts with endothelial cells on blood vessels to produce and excess of superoxide radicals, with attendant alterations in endothelial structure and function. The superoxide radical can scavenge endothelium-derived relaxing factor and produce potent oxidizing agents, which can cause lipid peroxidation and other degenerative changes. The alterations in vascular tone and endothelial damage are prevented by the oxygen-radical-scavenging enzyme superoxide dismutase. These observations suggest a normal vasoactive role for beta-amyloid as well as a mechanism by which beta-amyloid may play a role in vascular abnormalities and neurodegeneration mediated by free radicals.

Disruption of the p70(s6k)/p85(s6k) gene reveals a small mouse phenotype and a new functional S6 kinase

Recent studies have shown that the p70(s6k)/p85(s6k) signaling pathway plays a critical role in cell growth by modulating the translation of a family of mRNAs termed 5'TOPs, which encode components of the protein synthetic apparatus. Here we demonstrate that homozygous disruption of the p70(s6k)/p85(s6k) gene does not affect viability or fertility of mice, but that it has a significant effect on animal growth, especially during embryogenesis. Surprisingly, S6 phosphorylation in liver or in fibroblasts from p70(s6k)/p85(s6k)-deficient mice proceeds normally in response to mitogen stimulation. Furthermore, serum-induced S6 phosphorylation and translational up-regulation of 5'TOP mRNAs were equally sensitive to the inhibitory effects of rapamycin in mouse embryo fibroblasts derived from p70(s6k)/p85(s6k)-deficient and wild-type mice. A search of public databases identified a novel p70(s6k)/p85(s6k) homolog which contains the same regulatory motifs and phosphorylation sites known to control kinase activity. This newly identified gene product, termed S6K2, is ubiquitously expressed and displays both mitogen-dependent and rapamycin-sensitive S6 kinase activity. More striking, in p70(s6k)/p85(s6k)-deficient mice, the S6K2 gene is up-regulated in all tissues examined, especially in thymus, a main target of rapamycin action. The finding of a new S6 kinase gene, which can partly compensate for p70(s6k)/p85(s6k) function, underscores the importance of S6K function in cell growth.

Prostate stem cell antigen: a cell surface marker overexpressed in prostate cancer

The identification of cell surface antigens is critical to the development of new diagnostic and therapeutic modalities for the management of prostate cancer. Prostate stem cell antigen (PSCA) is a prostate-specific gene with 30% homology to stem cell antigen 2, a member of the Thy-1/Ly-6 family of glycosylphosphatidylinositol (GPI)-anchored cell surface antigens. PSCA encodes a 123-aa protein with an amino-terminal signal sequence, a carboxyl-terminal GPI-anchoring sequence, and multiple N-glycosylation sites. PSCA mRNA expression is prostate-specific in normal male tissues and is highly up-regulated in both androgen-dependent and -independent prostate cancer xenografts. In situ mRNA analysis localizes PSCA expression in normal prostate to the basal cell epithelium, the putative stem cell compartment of the prostate. There is moderate to strong PSCA expression in 111 of 126 (88%) prostate cancer specimens examined by in situ analysis, including high-grade prostatic intraepithelial neoplasia and androgen-dependent and androgen-independent tumors. Flow cytometric analysis demonstrates that PSCA is expressed predominantly on the cell surface and is anchored by a GPI linkage. Fluorescent in situ hybridization analysis localizes the PSCA gene to chromosome 8q24.2, a region of allelic gain in more than 80% of prostate cancers. A mouse homologue with 70% amino acid identity and similar genomic organization to human PSCA has also been identified. These results support PSCA as a target for prostate cancer diagnosis and therapy.

Rapamycin selectively represses translation of the "polypyrimidine tract" mRNA family

The immunosuppressant rapamycin blocks p70s6k/p85s6k activation and phosphorylation of 40S ribosomal protein S6 in Swiss 3T3 cells. The same net result is obtained when the macrolide is added 3 hr after serum stimulation. In stimulated cells p70s6k/p85s6k inactivation is achieved within minutes, whereas S6 dephosphorylation requires 1-2 hr, supporting the concept that S6 dephosphorylation results from kinase inactivation. In parallel, rapamycin treatment causes a small, but significant, reduction in the initiation rate of protein synthesis, as measured both by [35S]methionine incorporation into protein and by recruitment of 80S ribosomes into polysomes. More striking, analysis of individual mRNA transcripts revealed that rapamycin selectively suppresses the translation of a family of mRNAs that is characterized by a polypyrimidine tract immediately after their N7-methylguanosine cap, a motif that can act as a translational modulator. This family includes transcripts for ribosomal proteins, elongation factors of protein synthesis, and proteins of as-yet-unknown function. The results imply that (i) 40S ribosomes containing phosphorylated S6 may selectively recognize this motif or proteins which bind to it and (ii) rapamycin may inhibit cell growth by blocking S6 phosphorylation and, thus, translation of these mRNAs.

Influenza virus hemagglutinin with multibasic cleavage site is activated by furin, a subtilisin-like endoprotease

Many viruses have membrane glycoproteins that are activated at cleavage sites containing multiple arginine and lysine residues by cellular proteases so far not identified. The proteases responsible for cleavage of the hemagglutinin of fowl plague virus, a prototype of these glycoproteins, has now been isolated from Madin-Darby bovine kidney cells. The enzyme has a mol. wt of 85,000, a pH optimum ranging from 6.5 to 7.5, is calcium dependent and recognizes the consensus sequence R-X-K/R-R at the cleavage site of the hemagglutinin. Using a specific antiserum it has been identified as furin, a subtilisin-like eukaryotic protease. The fowl plague virus hemagglutinin was also cleaved after coexpression with human furin from cDNA by vaccinia virus vectors. Peptidyl chloroalkylketones containing the R-X-K/R-R motif specifically bind to the catalytic site of furin and are therefore potent inhibitors of hemagglutinin cleavage and fusion activity.

The modular phosphorylation and activation of p70s6k

The activation of p70s6k is accompanied by a complex series of phosphorylation events. In this review we propose a model of activation which divides p70s6k into four functional modules that cooperate in leading to full enzyme activity. In the light of the model, we suggest how candidate effectors of p70s6k activation might function by directing the phosphorylation of specific sites.

Genetic alterations associated with hepatocellular carcinomas define distinct pathways of hepatocarcinogenesis

BACKGROUND & AIMS

To evaluate how characterization of genetic alterations can help in the elucidation of liver carcinogenesis pathways, 137 tumors were analyzed.

METHODS

High-density allelotype, p53, Axin1, and beta-catenin gene mutations were determined. Alterations were analyzed according to clinical parameters.

RESULTS

Tumors could be divided into 2 groups according to chromosome stability status. In the first group, demonstrating a chromosome stability, beta-catenin mutation associated with chromosome 8p losses were frequently found as the single genetic alterations. beta-catenin mutations were associated with large tumor size and with negative hepatitis B virus status. In the second group, demonstrating a chromosome instability, the most frequent allelic losses were on chromosome 1p, 4q, 6q, 9p, 13q, 16p, 16q, and 17p; Axin1 and p53 were frequently mutated. All of these alterations, except losses on 6q and 9p, were associated with hepatitis B virus infection. P53 mutations, 17p, 13q losses, and a high value of the fractional allelic loss index were associated with poor differentiated tumors, independently of risk factors. Finally, in the whole series, chromosome 9p and 6q losses were associated with poor prognosis.

CONCLUSIONS

Two main pathways defined by genetic alterations show different risk factors and clinical characteristics. Furthermore, loss of chromosome 9p or 6q is an independent prognostic indicator.

Ewing sarcoma 11;22 translocation produces a chimeric transcription factor that requires the DNA-binding domain encoded by FLI1 for transformation

The 11;22 chromosomal translocation specifically linked to Ewing sarcoma and primitive neuroectodermal tumor results in a chimeric molecule fusing the amino-terminal-encoding portion of the EWS gene to the carboxyl-terminal DNA-binding domain encoded by the FLI1 gene. We have isolated a fourth EWS-FLI1 fusion cDNA that is structurally distinct from the three forms previously described. To determine the transforming activity of this gene, alternative forms of the EWS-FLI1 fusion were transduced into NIH 3T3 cells. Cells expressing either type 1 or type 4 fusion constructs formed foci in culture and colonies in soft agar, indicating that EWS-FLI1 is a transforming gene. EWS-FLI1 deletion mutants were created to map functionally the critical regions within the chimera. Deletion of either the EWS domain or the FLI1 corresponding to the DNA-binding domain totally abrogated the ability for EWS-FLI1 to transform 3T3 cells. These data indicate that the oncogenic effect of the 11;22 translocation is caused by the formation of a chimeric transcription factor. Formation of chimeric transcription factors has now been demonstrated to promote tumors of both neuroectodermal and hematopoietic origin, suggesting that this may be a common mechanism in human carcinogenesis.

Evidence for the complete inactivation of the NF2 gene in the majority of sporadic meningiomas

Meningiomas are common central nervous system tumours which present usually in the 4th and 5th decades of life. Loss of constitutional heterozygosity on chromosome 22 in 60% of sporadic meningiomas has implied the involvement of a tumour suppressor gene. The neurofibromatosis type 2 gene (NF2), a prime candidate for involvement in meningioma, was screened for point mutations. After examining eight of the 16 known NF2 exons in 151 meningiomas, 24 inactivating mutations were characterized. Significantly, these aberrations were exclusively detected in tumours which lost the other chromosome 22 allele. These results provide strong evidence that the suppressor gene on chromosome 22, frequently inactivated in meningioma, is the NF2 gene, and suggest that another gene is involved in the development of 40% of meningiomas.

Hypoinsulinaemia, glucose intolerance and diminished beta-cell size in S6K1-deficient mice

Insulin controls glucose homeostasis by regulating glucose use in peripheral tissues, and its own production and secretion in pancreatic beta cells. These responses are largely mediated downstream of the insulin receptor substrates, IRS-1 and IRS-2 (refs 4-8), through distinct signalling pathways. Although a number of effectors of these pathways have been identified, their roles in mediating glucose homeostasis are poorly defined. Here we show that mice deficient for S6 kinase 1, an effector of the phosphatidylinositide-3-OH kinase signalling pathway, are hypoinsulinaemic and glucose intolerant. Whereas insulin resistance is not observed in isolated muscle, such mice exhibit a sharp reduction in glucose-induced insulin secretion and in pancreatic insulin content. This is not due to a lesion in glucose sensing or insulin production, but to a reduction in pancreatic endocrine mass, which is accounted for by a selective decrease in beta-cell size. The observed phenotype closely parallels those of preclinical type 2 diabetes mellitus, in which malnutrition-induced hypoinsulinaemia predisposes individuals to glucose intolerance.

Clinical features of adrenocortical carcinoma, prognostic factors, and the effect of mitotane therapy

Adrenocortical carcinoma is a rare tumor, and only limited information is available about its natural history and the effects of therapy. We studied 105 patients (75 female and 30 male; mean age, 46 years) with adrenocortical carcinoma who were referred to us between 1963 and 1987. The average duration of symptoms before diagnosis was 8.7 months. At the time of diagnosis, 68 percent of the patients had endocrine symptoms, and 30 percent had distant metastases. Hormonal studies showed that 79 percent of the tumors were functional. Eighty patients underwent surgery, and 59 also received the adrenal cytotoxic agent mitotane. The median disease-free interval after surgery was 12.1 months (range, 1 to 175). Tumor dissemination occurred in 82 percent of the patients, most commonly to the lung, liver, and adjacent organs. The median survival time was 14.5 months (range, less than 1 to 175), and the five-year survival was 22 percent. Age over 40 years and the presence of metastases at the time of diagnosis were the only factors recognized as indicating a poor prognosis. Mitotane controlled hormonal secretion in 75 percent of the patients. Eight mitotane-treated patients had partial tumor regression, but the drug did not have a significant effect on survival. We conclude that adrenocortical carcinoma carries a poor prognosis. Mitotane therapy may offer transient benefits, particularly in controlling endocrine symptoms.

TOR signalling and control of cell growth

TOR, phosphatidylinositol 3-kinase, p70s6k, and 4E-BP1 have recently emerged as components of a major signalling pathway that is dedicated to protein translation and thus to cell growth. This pathway appears to be conserved, at least in part, in yeast, slime molds, plants, flies, and mammals. TOR and phosphatidylinositol 3-kinase control p70s6k and 4E-BP1, which, in turn, directly control the translation initiation machinery.