A sporulation-specific sigma factor of Bacillus subtilis ('E) is formed by a proteolytic activation of a precursor protein (P3l). Synthesis of the precursor protein is shown to be abolished in B. subtilis mutants with plasmid insertions as far as 940 base pairs upstream of the P31 structural gene (sigE), and processing of p3l to {rE is blocked by a deletion in this upstream region. These results substantiate the view that sigE is the distal member of a 2-gene operon and demonstrate that the upstream gene (spolIGA) is necessary for ifE formation.Bacillus subtilis responds to carbon, nitrogen, or phosphate deprivation with a program of sequential gene activation which transforms vegetatively growing bacteria into dormant endospores. At least a part of the mechanism for the proper activation of sporulation-specific genes is believed to occur through modifications to the DNA-dependent RNA polymerase of the developing cell (9). The bestcharacterized sporulation-specific RNA polymerase modification involves the association of a novel sigma factor (0rE, formerly a29) with the core enzyme (2,4,8 Synthesis of (rE is highly regulated. Transcription of the spoIIg operon commences only after the onset of sporulation and is dependent on a number of stage 0 sporulation gene products (5, 16). Aside from transcriptional regulation, a.E synthesis is controlled posttranslationally. The primary product of sigE translation is not C.E, but rather an inactive precursor protein (p31) (17). 0.E is derived from the precursor by a proteolytic modification which removes 29 amino acids from the P31 amino terminus (7). The activity responsible for processing p3' to a0E appears in sporulating cells between 1 and 2 h (Tl to T2) into development and is itself under spore gene control (18). We had previously noted that mutations at the spoIIE locus permitted the synthesis of p31 but not its processing (18). Recently, an analysis of the organization of the spoIIG operon provided evidence that spoIIG consists of two sporulation-essential genes: a promoter-proximal gene spoIIGA and a promoter-distal gene sigE (5).In this report we demonstrate directly that p31 synthesis does not occur if plasmid insertions interrupt the upstream region of the spoIIG operon; we also show that an upstream gene, spoIIGA, is essential for the processing of p31 to c29.The spoIIG operon therefore defines both the structural gene for 0.E and a gene which participates in its synthesis. MATERIALS AND METHODSBacterial strains and plasmids. B. subtilis SMY (trpC), JH642 (trpC2 phe-1), and SL608 (spoIIG49 leuA8 tal-J) were * Corresponding author. obtained from R. Losick, J. Hoch, and P. Piggot, respectively. BS50 (metC3 tal-J spoIIG4J) and the plasmids pGSIIG3 and pGSIIG12 were from J. Szulmajster. B. subtilis EU8722, EU8723, EU8724, EU8719, EU8739, EU8725, and EU8737 carrying integrated plasmids have been described previously (5). Expression of cloned sigE in the plasmid and bacteriophage vectors appears to depend on transcription initiating within the vector sequences. This...

Abstract:We investigate the constructions of tail-biting trellises for linear block codes introduced by Koetter/Vardy [9] and Nori/Shankar [15]. For a given code we will define the sets of characteristic generators more generally than in [9] and we will investigate how the choice of characteristic generators affects the set of resulting product trellises, called KV-trellises. Furthermore, we will show that each KV-trellis is a BCJR-trellis, defined in a slightly stronger sense than in [15], and that the latter are always non-mergeable. Finally, we will address a duality conjecture of Koetter/Vardy by making use of a dualization technique of BCJR-trellises and prove the conjecture for minimal trellises.

The oxazolidinones are a novel class of antimicrobial agents that target protein synthesis in a wide spectrum of gram-positive and anaerobic bacteria. The oxazolidinone PNU-100766 (linezolid) inhibits the binding of fMet-tRNA to 70S ribosomes. Mutations to oxazolidinone resistance in Halobacterium halobium, Staphylococcus aureus, and Escherichia coli map at or near domain V of the 23S rRNA, suggesting that the oxazolidinones may target the peptidyl transferase region responsible for binding fMet-tRNA. This study demonstrates that the potency of oxazolidinones corresponds to increased inhibition of fMet-tRNA binding. The inhibition of fMettRNA binding is competitive with respect to the fMet-tRNA concentration, suggesting that the P site is affected. The fMet-tRNA reacts with puromycin to form peptide bonds in the presence of elongation factor P (EF-P), which is needed for optimum specificity and efficiency of peptide bond synthesis. Oxazolidinone inhibition of the P site was evaluated by first binding fMet-tRNA to the A site, followed by translocation to the P site with EF-G. All three of the oxazolidinones used in this study inhibited translocation of fMet-tRNA. We propose that the oxazolidinones target the ribosomal P site and pleiotropically affect fMet-tRNA binding, EF-P stimulated synthesis of peptide bonds, and, most markedly, EF-G-mediated translocation of fMet-tRNA into the P site.A novel class of antimicrobial agents, the oxazolidinones, target a wide spectrum of gram-positive and anaerobic bacteria (4, 6, 9, 28). These compounds act by inhibiting protein synthesis and have no effect on replication or transcription (8). Cell extracts exposed to oxazolidinones are impaired in protein synthesis when programmed by native mRNAs but do not appear to be inhibited when programmed by synthetic mRNAs that lack the signals required for initiation and termination of translation (7,8,26). This suggested that these compounds may target the initiation reaction. The oxazolidinone PNU-100766 (linezolid; Fig. 1) inhibits binding of the initiator fMettRNA to the 70S ribosomal particle programmed with a synthetic mRNA that harbors a Shine-Dalgarno sequence and a properly spaced initiation codon (29).Mutations to oxazolidinone resistance map to domain V of the 23S rRNA in Halobacterium halobium (18), Staphylococcus aureus (27), and the enterococci while mapping to domains IV and V in Escherichia coli (33). The position of these PNU-100766 resistance mutations suggested to us that the oxazolidinones may target peptidyl transferase indirectly by affecting the binding of the initiator tRNA. Since the P site accommodates the initiator tRNA and the nascent protein, these drugs could also affect the affinity of the peptidyl-tRNA for the ribosome.Recent studies have indicated that the oxazolidinones bind to 70S ribosomes, as well as to 50S subunits (19), but not to 30S subunits. In contrast, a report by Matassova et al. (20) demonstrated that oxazolidinone footprints map to the central domain of the 16S rRNA whereas the 23S rRNA ...

Descending necrotising mediastinitis is a rare and serious infection with a high mortality rate, which complicates pharyngeal or odontogenic infection. Early recognition and treatment are essential in order to minimise morbidity. Evaluation with computed tomography is necessary to confirm the diagnosis and facilitate surgical planning. In addition to prompt empirical antiobiotic therapy, surgical intervention is necessary in nearly all cases. Surgical drainage and debridement may be performed through cervicotomy alone, or through combined cervicotomy and thoracotomy, depending upon the extent of disease. Hyperbaric oxygen therapy may play an auxiliary role. We present two recent cases with characteristic imaging findings, and review the relevant literature. KEYWORDS: Computed tomography, mediastinitis CASE ONEA 60-yr-old male presenting with neck swelling, dysphagia and hoarseness had been extubated 2 days previously following a pneumonia. He had a past medical history of laryngeal cancer treated 10 yrs ago with external beam radiation and chemotherapy. On examination he had bilateral diffuse neck erythema, oedema and right-sided induration. Fibre-optic laryngoscopy showed scabbing of the right hypopharynx and erythematous swelling of the false vocal folds, aryepiglottic folds, and epiglottis. Over the course of 12 h, he developed septic shock with a blood pressure of 70/ 30 mmHg, heart rate of 135 beats?min, and a temperature of 103uF. He was started empirically on vancomycin and piperacillin/tazobactam. After stabilisation in the intensive care unit (ICU), computed tomography (CT) imaging of the neck and chest was performed. There was a large amount of subcutaneous air tracking into the deep fascial planes of the anterior neck, oedematous laryngeal mucosa, and bilateral loculated fluid collections tracking throughout the anterior neck extending to the superior mediastinum ( fig. 1). CT imaging of the chest showed a complex air and fluid collection in the anterior mediastinum extending to the base of the neck ( fig. 2). After review of the images, the patient was taken to the operating room for a combined procedure performed by both head and neck surgeons and thoracic surgeons. Bilateral anterior neck dissections were performed, and blunt dissection, irrigation and debridement were carried out to several centimeters below the sternal manubrium. Penrose drains were left in place. Then, left anterior thoracotomy with debridement of the anterior mediastinum, left pleural decortication and a pericardial window were performed by the thoracic surgeons. Microbiology of the anterior mediastinal fluid grew multiple organisms including Fusobacterium, Prevotella, Bacteroides fragilis, Peptostreptococcus, and a heavy growth of Streptococcus intermedius. Pathology of the pharyngeal lesions showed necrosis and granulation tissue. No neoplasm was identified. The patient later received a tracheostomy and pectoralis myocutaneous flap repair of the neck without sequelae. His total ICU length of stay was 32 days, and hi...

This paper focuses on dualizing tail-biting trellises, particularly KV-trellises. These trellises are based on characteristic generators, as introduced by Koetter/Vardy (2003), and may be regarded as a natural generalization of minimal conventional trellises, even though they are not necessarily minimal. Two dualization techniques will be investigated: the local dualization, introduced by Forney (2001) for general normal graphs, and a linear algebra based dualization tailored to the specific class of tail-biting BCJR-trellises, introduced by Nori/Shankar (2006). It turns out that, in general, the BCJR-dual is a subtrellis of the local dual, while for KV-trellises these two coincide. Furthermore, making use of both the BCJR-construction and the local dualization, it will be shown that for each complete set of characteristic generators of a code there exists a complete set of characteristic generators of the dual code such that their resulting KV-trellises are dual to each other if paired suitably. This proves a stronger version of a conjecture formulated by Koetter/Vardy.