Cor Adiposum as the Cause of Sudden Cardiac Death: A Case Report and Literature Review

We present a case of sudden cardiac death in a 65-year-old patient who came to the emergency room with shortness of breath. The gross examination of the heart was significant for extensive left ventricular lipomatosis in association with myocardial fibrosis. Microscopic examination revealed extensive fatty replacement of the myocardial tissue throughout the entire thickness of the ventricular wall (transmural lipomatous myocardial remodeling). We suggest using the term "cor adiposum" to categorize this morphological condition when the transmural lipomatous transformation of the myocardium is present. The fatty replacement of the heart muscle would have led to impaired cardiac function, ultimately resulting in sudden cardiac death in this patient. We also hypothesize that the accumulation of fat in the myocardium might be a compensatory process to preserve ventricular wall compliance.

Diffuse Alveolar Hemorrhage Occurring Suddenly in a Diabetic Patient With Asthma Exacerbation

Diffuse alveolar hemorrhage (DAH) is a rare but potentially life-threatening condition characterized by bleeding into the alveolar spaces of the lungs. DAH can occur due to a wide range of etiologies including autoimmune diseases, infections, drugs, and malignancies. The clinical presentation is variable and may include cough, dyspnea, fever, and hemoptysis. Diagnosis is often challenging due to the nonspecific symptoms and a lack of definitive diagnostic criteria. Treatment is primarily aimed at addressing the underlying cause and providing supportive care.

Massive Hemorrhage Following Spontaneous Mediastinal Inflammatory Myofibroblastic Tumor Rupture: A Case Report

A 45-year-old male in a hypertensive emergency was admitted with complaints of frontal headache, progressive chest discomfort, shortness of breath, dysphagia, and right upper quadrant abdominal pain radiating across the epigastrium and to the back that increases in intensity with deep inspiration. He denied any history of abdominal pain, vomiting, dyspnea, nausea, and weight loss. A computed tomography (CT) scan of the chest showed a posterior mediastinal mass between the esophagus and descending aorta. A magnetic resonance imaging (MRI) scan revealed a non-enhancing posterior mediastinal mass possibly compressing both the esophagus and the airway. A 30-degree thoracoscope was inserted in the chest cavity revealing a large hemothorax from a possibly ruptured inflammatory myofibroblastic tumor (IMT) encompassing nearly the entire pleural space with both fresh and clotted blood. Two liters of fresh blood was removed via a right thoracotomy procedure. Once removed, a large fibrinous clot-filled mass was resected entirely and sent to pathology. Postoperative recovery was uneventful; dysphagia and shortness of breath resolved. The patient gradually resumed his regular diet.

Ectopic Cushing Syndrome in Adenocarcinoma of the Lung: Case Report and Literature Review

Paraneoplastic syndromes are rare disorders that occur with many types of tumors. Ectopic cushing syndrome (ECS) is the second most common paraneoplastic syndrome that is only seen in 1-5% of all small cell lung cancers (SCLC), with limited papers reporting this syndrome since it was first described by Brown in 1928 or in carcinoid tumors. It is also found to be associated to a lesser extent with pheochromocytoma, thymic tumors, pancreatic carcinoma, and anaplastic thyroid carcinoma. While lung adenocarcinoma is the most common histological type of lung neoplasms, it is seldom associated with Cushing syndrome. In this article, we describe a patient who initially presented with Cushing syndrome and found to have adenocarcinoma of the lung.

Unique presentation of occult breast cancer with uterine cervix metastasis

We are reporting a case of occult breast cancer (OBC) diagnosed via biopsy of an asymptomatic cervical mass. While non-OBC has occasionally been reported as metastatic to the uterine cervix, OBC never has, to our knowledge. Awareness of this presentation can be beneficial for a more expedite diagnosis and treatment.

Significance of pigmented urothelial and non-urothelial cells in voided urine specimens: A case report and review

We present a case of metastatic malignant melanoma to the urinary bladder diagnosed on a voided urinary cytology specimen in a patient who visited the emergency department complaining of right flank pain, and dark urine. The patient reported having previous episodes of kidney stones. Additionally, more detailed clinical history obtained after the cytological diagnosis, revealed a previous excision of malignant melanoma on the back 10 years ago. The diagnosis of metastatic malignant melanoma was based solely on voided urine cytology. While metastases of malignant melanoma to urinary bladder are well known, the significance of pigmented cells in voided urine specimens is not well documented. In this article we provide a discussion as well as a review of the literature about possible disease entities associated with pigment containing urothelial as well as non-urothelial cells.

Adult rhabdomyosarcoma of the maxillary sinus with orbital extension

A 40-year-old male presented with 2 weeks of left facial pain, nasal congestion, dysphonia, and epistaxis along with left-sided epiphora. CT showed a large infiltrative mass centered in the left maxillary sinus with extension into the left orbit, bilateral paranasal sinuses, nasal cavity, and bilateral enlarged cervical lymph nodes. Biopsy results confirmed adult alveolar rhabdomyosarcoma (RMS). Systemic workup confirmed bilateral cervical lymph node metastasis. Currently the patient is undergoing chemotherapy. We describe a rare case of adult paranasal sinus RMS with orbital invasion.

Case report of undifferentiated endometrial sarcoma in association with osteoclast-like giant cells

We describe the clinical, gross and microscopic features of undifferentiated uterine stromal sarcoma associated with osteoclast-like giant cells. A case of low-grade endometrial stromal sarcoma is already described in association with osteoclast-like giant cells; however, the current case differs in that the tumor was a high grade and did not show any evidence of smooth muscle or epithelioid differentiation and was shown to be strongly positive for CD10 and focally for WT-1 and Inhibin supporting an endometrial stromal origin. The associated osteoclast-like giant cells were abundant, evenly distributed within the tumor and showed strong positivity for CD68. Interestingly, rare (less than 2%) giant cells also showed weak cytoplasmic positivity for b-hCG. The tumor infiltrated deep into the myometrium and had marked lymphovascular invasion. Although the regional lymph nodes and peritoneal washings were negative, the lesion showed a highly aggressive clinical course. Despite treatment, the tumor disseminated within the abdominal cavity and lungs and ultimately led to the patient's demise within 9 months of the diagnosis.

Computer-assisted image analysis of amyloid deposits in abdominal fat pad aspiration biopsies

Amyloidosis is a heterogeneous group of diseases with a common outcome: deposition of insoluble protein in the visceral organs and tissues. Primary amyloidosis is a consequence of different plasma cell disorders, and it is the most common form of amyloidosis in the United States with an estimated 2,000 new cases annually. Other forms of amyloidosis include chronic inflammatory processes, familial type of amyloidosis, and localized forms like Alzheimer's disease.The diagnosis of amyloidosis is based on the clinical picture and demonstration of amyloid deposit in tissues with Congo-red stain. In our article, we describe a simple methodology for image analysis of fat pad biopsies for amyloidosis using a commercially available software Adobe Photoshop CS3(c) Extended Edition. The principle is based on calculation of the mean gray value of each blue and green channel and comparison of their ratios. As a negative control, we have used samples from heart, scar tissue, and skin with their representative control. Fibrous tissue often gives a white:blue to blue:green birefringence, which often is confused with the apple: green birefringence of the amyloid stain; however, we were successful in discriminating these colors using the methodology described in this article. We also analyzed 22 patients with at least 2 years follow-up in our institution. The specificity and the sensitivity of the computer-assisted image analysis were calculated to be 75% and 100%, respectively. These results are in agreement with the published papers (references here); however, caution should be exercised before drawing firm conclusions because of the small sample size presented here.

Fine-needle aspiration biopsy of metastatic malignant melanoma resembling a malignant peripheral nerve sheath tumor

We report a case of metastatic malignant melanoma resembling a malignant peripheral sheath tumor, which posed a significant diagnostic challenge. The patient is a 76-year-old male, who presented in the emergency room with bilateral chest pain exacerbated by inspiration. The pain was present for 3 week and was not exacerbated by physical exercise. The diagnostic workup revealed bilateral parenchymal pulmonary infiltrates. The CT-scan guided fine-needle aspiration and the core biopsies of the largest pulmonary lesion revealed high-grade spindle cell neoplasm with individual cell apoptosis and necrosis. The immunohistochemical profile on the cell block showed that the cells are positive for Vimentin. The S-100 stain showed only focal positivity. The immunohistochemical stains for HMB45, Melan A, pancytokeratin, and smooth muscle actin were negative. Five years ago the patient was diagnosed with melanoma on the back with Clark level of IV. The melanoma was excised with clear margins and sentinel lymph nodes were negative. Careful examination of patient's previous slides revealed an area of spindle cell melanoma adjacent to a nodular type melanoma. Based on the patient's previous history, current clinico-pathologic presentation and immunohistochemical profile, the diagnosis of metastatic malignant melanoma resembling peripheral nerve sheath tumor was favored over the diagnosis of metastatic malignant spindle cell neoplasm of unknown primary site, which by itself is very rare clinical scenario.

Protection elicited by two glutamine auxotrophs of Mycobacterium tuberculosis and in vivo growth phenotypes of the four unique glutamine synthetase mutants in a murine model

We generated four individual glutamine synthetase (GS) mutants (DeltaglnA1, DeltaglnA2, DeltaglnA3, and DeltaglnA4) and one triple mutant (DeltaglnA1EA2) of Mycobacterium tuberculosis to investigate the roles of GS enzymes. Subcutaneous immunization with the DeltaglnA1EA2 and DeltaglnA1 glutamine auxotrophic mutants conferred protection on C57BL/6 mice against an aerosol challenge with virulent M. tuberculosis, which was comparable to that provided by Mycobacterium bovis BCG vaccination.

Molecular aspects of diagnostic nucleolar and nuclear envelope changes in prostate cancer

Prostate cancer is still diagnosed by pathologists based on subjective assessment of altered cell and tissue structure. The cellular-level structural changes diagnostic of some forms of cancer are known to be induced by cancer genes, but the relation between specific cellular-level structural features and cancer genes has not been explored in the prostate. Two important cell structural changes in prostate cancer-nucleolar enlargement and nuclear envelope (NE) irregularity-are discussed from the perspective that they should also relate to the function of the genes active in prostate cancer. Enlargement of the nucleolus is the key diagnostic feature of high-grade prostatic intraepithelial neoplasia (PIN), an early stage that appears to be the precursor to the majority of invasive prostate cancers. Nucleolar enlargement classically is associated with increased ribosome production, and production of new ribosomes appears essential for cell-cycle progression. Several cancer genes implicated in PIN are known (in other cell types) to augment ribosome production, including c-Myc, p27, retinoblastoma, p53, and growth factors that impact on ERK signaling. However, critical review of the available information suggests that increased ribosome production per se may be insufficient to explain nucleolar enlargement in PIN, and other newer functions of nucleoli may therefore need to be invoked. NE irregularity develops later in the clonal evolution of some prostate cancers, and it has adverse prognostic significance. Nuclear irregularity has recently been shown to develop dynamically during interphase following oncogene expression, without a requirement for post-mitotic NE reassembly. NE irregularity characteristic of some aggressive prostate cancers could reflect cytoskeletal forces exerted on the NE during active cell locomotion. NE irregularity could also promote chromosomal instability because it leads to chromosomal asymmetry in metaphase. Finally, NE irregularity could impact replication competence, transcriptional programming and nuclear pore function.

Rapid identification and susceptibility testing of Mycobacterium tuberculosis from MGIT cultures with luciferase reporter mycobacteriophages

In a prospective study conducted in a diagnostic laboratory in Mexico City, luciferase reporter mycobacteriophages (LRPs) were evaluated for their utility and performance in identification and antibiotic-susceptibility testing of Mycobacterium tuberculosis complex (MTC) isolates from MGIT-960 cultures. Eighty-four consecutive MGIT cultures recovered from 54 patients were included in this study. The LRPs confirmed mycobacterial growth in 79 (94 %) of 84 MGIT cultures. Failure to confirm growth was due to low inoculum (n = 1) or growth with non-tuberculous mycobacteria (n = 4). The median time to confirmation of MGIT cultures was 1 day (range 1-55). Confirmed cultures were identified with p-nitro-alpha-acetylamino-beta-hydroxypropiophenone (NAP), a selective inhibitor of MTC species, and results obtained with LRPs were compared with those obtained by BACTEC-460. The sensitivity and specificity of the LRP NAP test were respectively 97 and 100 %, and the median turnaround time for identification was 3 days with both methods. The accuracy and speed of the LRPs for susceptibility testing with rifampicin, streptomycin, isoniazid and ethambutol were compared with BACTEC-460 and discrepant results were tested by the conventional agar proportion method. In total, 72 MTC cultures were tested. The overall agreement between the LRPs and BACTEC-460 was 98.6 %. Four isolates (5.6 %) were falsely identified as ethambutol-resistant. The median turnaround time for susceptibility testing was 3 days (range 3-57) with the LRPs and 9 days (range 7-29) with BACTEC-460. LRPs offer an accurate and rapid approach for identification and susceptibility testing of M. tuberculosis from MGIT-960 cultures.

Detection and drug-susceptibility testing of M. tuberculosis from sputum samples using luciferase reporter phage: comparison with the Mycobacteria Growth Indicator Tube (MGIT) system

Rapid diagnosis of drug-resistant M.tuberculosis (Mtb) is desirable worldwide. We (i) describe a new luciferase reporter phage (LRP), phAE142 for this purpose; (ii) compare it to the automated MGIT 960 for time-to-detection of Mtb in clinical specimens; and (iii) evaluate its use for species confirmation and antibiotic susceptibility testing(AST) of Mtb. Twenty sputum samples were inoculated for testing by LRP, or by MGIT 960. After "positives" were identified by either method, the LRP was used for confirmation of Mtb complex (TBC) and for AST. The LRP method proved comparably efficient to MGIT 960 at detecting Mtb. Using an antibiotic uniquely inhibiting TBC with LRP provided species assignment, concurrently with AST, in a median of 3 days, with a sensitivity of 97%. Overall agreement in susceptibility results was 96%. Reliable susceptibility results and identification of TBC can be completed in a median of 12 days (range 8 to 16d) with LRP applied to sputum samples.

Specialized transduction: an efficient method for generating marked and unmarked targeted gene disruptions in Mycobacterium tuberculosis, M. bovis BCG and M. smegmatis

The authors have developed a simple and highly efficient system for generating allelic exchanges in both fast- and slow-growing mycobacteria. In this procedure a gene of interest, disrupted by a selectable marker, is cloned into a conditionally replicating (temperature-sensitive) shuttle phasmid to generate a specialized transducing mycobacteriophage. The temperature-sensitive mutations in the mycobacteriophage genome permit replication at the permissive temperature of 30 degrees C but prevent replication at the non-permissive temperature of 37 degrees C. Transduction at a non-permissive temperature results in highly efficient delivery of the recombination substrate to virtually all cells in the recipient population. The deletion mutations in the targeted genes are marked with antibiotic-resistance genes that are flanked by gammadelta-res (resolvase recognition target) sites. The transductants which have undergone a homologous recombination event can be conveniently selected on antibiotic-containing media. To demonstrate the utility of this genetic system seven different targeted gene disruptions were generated in three substrains of Mycobacterium bovis BCG, three strains of Mycobacterium tuberculosis, and Mycobacterium smegmatis. Mutants in the lysA, nadBC, panC, panCD, leuCD, Rv3291c and Rv0867c genes or operons were isolated as antibiotic-resistant (and in some cases auxotrophic) transductants. Using a plasmid encoding the gammadelta-resolvase (tnpR), the resistance genes could be removed, generating unmarked deletion mutations. It is concluded from the high frequency of allelic exchange events observed in this study that specialized transduction is a very efficient technique for genetic manipulation of mycobacteria and is a method of choice for constructing isogenic strains of M. tuberculosis, BCG or M. smegmatis which differ by defined mutations.

Evidence that mycobacterial PE_PGRS proteins are cell surface constituents that influence interactions with other cells

The elucidation of the genomic sequence of Mycobacterium tuberculosis revealed the presence of a novel multigene family designated PE/PE_PGRS that encodes numerous, highly related proteins of unknown function. In this study, we demonstrate that a transposon insertion in a PE_PGRS gene (1818(PE_PGRS)) found in Mycobacterium bovis BCG Pasteur, which is the BCG homologue of the M. tuberculosis H37Rv gene Rv1818c, introduces new phenotypic properties to this BCG strain. These properties include dispersed growth in liquid medium and reduced infection of macrophages. Complementation of the 1818(PE_PGRS)::Tn5367 mutant with the wild-type gene restores both aggregative growth (clumping) in liquid medium and reestablishes infectivity of macrophages to levels equivalent to those for the parent BCG strain. Western blot analysis using antisera raised against the 1818(PE_PGRS) protein shows that PE_PGRS proteins are found in cell lysates of BCG and M. tuberculosis H37Ra and in the cell wall fraction of M. tuberculosis H37Rv. Moreover, immunofluorescent labeling of mycobacteria indicates that certain PE_PGRS proteins are localized at the cell surface of BCG and M. tuberculosis. Together these results suggest that certain PE_PGRS proteins may be found at the surface of mycobacteria and influence both cell surface interactions among mycobacteria as well as the interactions of mycobacteria with macrophages.

Luciferase reporter mycobacteriophages for detection, identification, and antibiotic susceptibility testing of Mycobacterium tuberculosis in Mexico

The utility of luciferase reporter mycobacteriophages (LRPs) for detection, identification, and antibiotic susceptibility testing of Mycobacterium tuberculosis was prospectively evaluated in a clinical microbiology laboratory in Mexico City, Mexico. Five hundred twenty-three consecutive sputum samples submitted to the laboratory during a 5-month period were included in this study. These specimens were cultivated in Middlebrook 7H9 (MADC), MGIT, and Löwenstein-Jensen (LJ) media. Of the 71 mycobacterial isolates recovered with any of the three media, 76% were detected with the LRPs, 97% were detected with the MGIT 960 method, and 90% were detected with LJ medium. When contaminated specimens were excluded from the analysis, the LRPs detected 92% (54 of 59) of the cultures. The median time to detection of bacteria was 7 days with both the LRPs and the MGIT 960 method. LRP detection of growth in the presence of p-nitro-alpha-acetylamino-beta-hydroxypropiophenone (NAP) was used for selective identification of M. tuberculosis complex (MTC) and compared to identification with BACTEC 460. Using the LRP NAP test, 47 (94%) out of 50 isolates were correctly identified as tuberculosis complex. The accuracy and speed of LRP antibiotic susceptibility testing with rifampin, streptomycin, isoniazid, and ethambutol were compared to those of the BACTEC 460 method, and discrepant results were checked by the conventional proportion method. In total, 50 MTC isolates were tested. The overall agreement between the LRP and BACTEC 460 results was 98.5%. The median LRP-based susceptibility turnaround time was 2 days (range, 2 to 4 days) compared to 10.5 days (range, 7 to 16 days) by the BACTEC 460 method. Phage resistance was not detected in any of the 243 MTC isolates tested. Mycobacteriophage-based approaches to tuberculosis diagnostics can be implemented in clinical laboratories with sensitivity, specificity, and rapidity that compare favorably with those of the MGIT 960 and BACTEC 460 methods. The phages currently provide the fastest phenotypic assay for susceptibility testing.

The alternative sigma factor SigH regulates major components of oxidative and heat stress responses in Mycobacterium tuberculosis

Mycobacterium tuberculosis is a specialized intracellular pathogen that must regulate gene expression to overcome stresses produced by host defenses during infection. SigH is an alternative sigma factor that we have previously shown plays a role in the response to stress of the saprophyte Mycobacterium smegmatis. In this work we investigated the role of sigH in the M. tuberculosis response to heat and oxidative stress. We determined that a M. tuberculosis sigH mutant is more susceptible to oxidative stresses and that the inducible expression of the thioredoxin reductase/thioredoxin genes trxB2/trxC and a gene of unknown function, Rv2466c, is regulated by sigH via expression from promoters directly recognized by SigH. We also determined that the sigH mutant is more susceptible to heat stress and that inducible expression of the heat shock genes dnaK and clpB is positively regulated by sigH. The induction of these heat shock gene promoters but not of other SigH-dependent promoters was markedly greater in response to heat versus oxidative stress, consistent with their additional regulation by a heat-labile repressor. To further understand the role of sigH in the M. tuberculosis stress response, we investigated the regulation of the stress-responsive sigma factor genes sigE and sigB. We determined that inducible expression of sigE is regulated by sigH and that basal and inducible expression of sigB is dependent on sigE and sigH. These data indicate that sigH plays a central role in a network that regulates heat and oxidative-stress responses that are likely to be important in M. tuberculosis pathogenesis.

Attenuation of and protection induced by a leucine auxotroph of Mycobacterium tuberculosis

Attenuated mutants of Mycobacterium tuberculosis represent potential vaccine candidates for the prevention of tuberculosis. It is known that auxotrophs of a variety of bacteria are attenuated in vivo and yet provide protection against challenge with wild-type organisms. A leucine auxotroph of M. tuberculosis was created by allelic exchange, replacing wild-type leuD (Rv2987c), encoding isopropyl malate isomerase, with a mutant copy of the gene in which 359 bp had been deleted, creating a strain requiring exogenous leucine supplementation for growth in vitro. The frequency of reversion to prototrophy was <10(-11). In contrast to wild-type M. tuberculosis, the DeltaleuD mutant was unable to replicate in macrophages in vitro. Its attenuation in vivo and safety as a vaccine were established by the fact that it caused no deaths in immunodeficient SCID mice. Complementation of the mutant with wild-type leuD abolished the requirement for leucine supplementation and restored the ability of the strain to grow both in macrophages and in SCID mice, thus confirming that the attenuated phenotype was due to the DeltaleuD mutation. As a test of the vaccine potential of the leucine auxotroph, immunocompetent BALB/c mice, susceptible to fatal infection with wild-type M. tuberculosis, were immunized with the DeltaleuD mutant and subsequently challenged with virulent M. tuberculosis by both the intravenous and aerosol routes. A comparison group of mice was immunized with conventional Mycobacterium bovis BCG vaccine. Whereas all unvaccinated mice succumbed to intravenous infection within 15 weeks, mice immunized with either BCG or the DeltaleuD mutant of M. tuberculosis exhibited enhanced and statistically equivalent survival curves. However, the leuD auxotroph was less effective than live BCG in reducing organ burdens and tissue pathology of mice challenged by either route. We conclude that attenuation and protection against M. tuberculosis challenge can be achieved with a leucine auxotroph and suggest that to induce optimal protection, attenuated strains of M. tuberculosis should persist long enough and be sufficiently metabolically active to synthesize relevant antigens for an extended period of time.

Rapid film-based determination of antibiotic susceptibilities of Mycobacterium tuberculosis strains by using a luciferase reporter phage and the Bronx Box

Detecting antibiotic resistance in Mycobacterium tuberculosis is becoming increasingly important with the global recognition of drug-resistant strains and their adverse impact on clinical outcomes. Current methods of susceptibility testing are either time-consuming or costly; rapid, reliable, simple, and inexpensive methods would be highly desirable, especially in the developing world where most tuberculosis is found. The luciferase reporter phage is a unique reagent well-suited for this purpose: upon infection with viable mycobacteria, it produces quantifiable light which is not observed in mycobacterial cells treated with active antimicrobials. In this report, we describe a modification of our original assay, which allows detection of the emitted light with a Polaroid film box designated the Bronx Box. The technique has been applied to 25 M. tuberculosis reference and clinical strains, and criteria are presented which allow rapid and simple discrimination among strains susceptible or resistant to isoniazid and rifampin, the major antituberculosis agents.

Conditionally replicating luciferase reporter phages: improved sensitivity for rapid detection and assessment of drug susceptibility of Mycobacterium tuberculosis

TM4 is a lytic mycobacteriophage which infects mycobacteria of clinical importance. A luciferase reporter phage, phAE40, has been constructed from TM4 and was previously shown to be useful for the rapid detection and drug susceptibility testing of Mycobacterium tuberculosis. However, the lytic nature of the phage results in a loss of detectable light output and limits the sensitivity of detection. We describe several strategies aimed at improving the luciferase activity generated by TM4 luciferase phages, including (i) varying the position of the luciferase gene in the phage genome, (ii) isolating host-range mutants of the phage, and (iii) introducing temperature-sensitive mutations in the phage such that it will not replicate at the infecting temperature. Several new phages generated by these methods show increased intensity of luciferase production compared to the first-generation reporter phage phAE40, and one phage, phAE88, also demonstrates an enhanced duration of luciferase activity. This has allowed the detection of as few as 120 BCG cells and the determination of drug susceptibilities of M. tuberculosis in as little as 1 day.

Conditionally replicating mycobacteriophages: a system for transposon delivery to Mycobacterium tuberculosis

Transposon mutagenesis provides a direct selection for mutants and is an extremely powerful technique to analyze genetic functions in a variety of prokaryotes. Transposon mutagenesis of Mycobacterium tuberculosis has been limited in part because of the inefficiency of the delivery systems. This report describes the development of conditionally replicating shuttle phasmids from the mycobacteriophages D29 and TM4 that enable efficient delivery of transposons into both fast- and slow-growing mycobacteria. These shuttle phasmids consist of an Escherichia coli cosmid vector containing either a mini-Tn10(kan) or Tn5367 inserted into a nonessential region of the phage genome. Thermosensitive mutations were created in the mycobacteriophage genome that allow replication at 30 degrees C but not at 37 degrees C (TM4) or 38.5 degrees C (D29). Infection of mycobacteria at the nonpermissive temperature results in highly efficient transposon delivery to the entire population of mycobacterial cells. Transposition of mini-Tn10(kan) occurred in a site-specific fashion in M. smegmatis whereas Tn5367 transposed apparently randomly in M. phlei, Bacille Calmette-Guérin (BCG), and M. tuberculosis. Sequence analysis of the M. tuberculosis and BCG chromosomal regions adjacent to Tn5367 insertions, in combination with M. tuberculosis genomic sequence and physical map data, indicates that the transpositions have occurred randomly in diverse genes in every quadrant of the genome. Using this system, it has been readily possible to generate libraries containing thousands of independent mutants of M. phlei, BCG, and M. tuberculosis.

Chemical synthesis and characteristics of a hybrid phage T5-lac promoter

A new P1O1R9 inducible promoter (where P1 is a promoter sequence analogous to that of the phage T5 early promoter; O1 is lac-operator; and R9 is a ribosome binding site) was synthesized. We studied the efficiency of this promoter in controlling and inducible gene expression using two model genes: human calcitonin tetrameric (hCT[4]) and human interferon alpha 1 (hIFN alpha 1). The synthetic lac-operator O1 was found to repress P1 activity in media free of lac-operon inducers which was derepressed in the presence of IPTG. The levels of expression of both genes (evaluated by quantitating mRNA and protein) in the presence of lac-inducers were close to those obtained with the P1R9 constitutive promoter.

Expression of repetitive human calcitonin genes in Escherichia coli

In order to stabilize recombinant human calcitonin (rhCT) against Escherichia coli proteases a series of concatemeric hCT genes with varying degrees of repetition were synthesized and expressed in E. coli under the control of a constitutive synthetic phage promoter. The series of expression vectors thus constructed was used as a model to study the effect of gene repetition on the efficiency of expression (both transcription and translation), stability of mRNA, proteolytic stability of recombinant protein, genetic stability of expression plasmids, etc. The oligomerization of the hCT gene resulted in stabilization of the mRNA increasing its half-life from 60-70 s (as in the hCT monomer, dimer, and trimer genes) to 100-120 s (for the hCT tetramer gene). This effect held true as well for the proteins coded by the corresponding repetitive hCT genes. The genetic stability (segregation and recombination) of the expression plasmids containing hCT oligomeric genes also depended on the number of hCT gene repeats. The expression plasmid containing the hCT tetramer gene segregated from one of the best producers of rhCT (E. coli LE392) up to 100% after 100 cell generations in nonselective media (free of antibiotics). One of the plasmids most sensitive to recombination events was that containing the hCT pentamer gene. The series of expression plasmids bearing hCT oligomeric genes was used for transformation of various E. coli strains in order to find the optimal host for production of rhCT. The highest yield (44-100 mg rhCT per 1 liter of bacterial culture) was obtained with the strains LE392, JM107, and DH1.

Is the nuclear matrix the site of DNA replication in eukaryotic cells?

Four types of experiment were carried out to test the recently proposed model of matrix-bound replication in eukaryotic cells. In experiments with pulse-labelling we found preferential association of newly replicated DNA with the matrix only when the procedure for isolation includes first high-salt treatment of isolated nuclei and then digestion with nucleases, or when prior to digestion the nuclei have been stored for a prolonged time. In both cases, however, evidence was found that this preferential association is due to a secondary, artifactual binding of the newly replicated chromatin region to the matrix elements. Pulse-chase experiments and experiments with continuous labelling were carried out to answer the question whether during replication the DNA is reeled through the replication complexes, i.e., whether newly replicated DNA is temporarily or permanently associated with the matrix. The results showed that at that time the matrix DNA does not move from its site of attachment. Since, according to the model of matrix-bound replication, the forks are assumed to be firmly anchored to high-salt resistant proteinaceous matrix structures, the chromatin fragments isolated with endonuclease not recognizing newly replicated DNA and purified by sucrose gradient centrifugation should be free of replication intermediates. The electronmicroscopic analysis of such fragments revealed the existence of intact replication micro-bubbles. Moreover, the fragments with replication configurations appeared as smooth chromatin fibres not attached to elements characteristic for the matrix. All these experiments suggest that the nuclear skeleton is not a native site of DNA replication in eukaryotic cells.