Outcome after second stem cell transplantation for relapsed multiple myeloma

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Background: Autologous stem cell transplantation (ASCT) improves survival and remains the standard of care for patients with newly diagnosed myeloma considered eligible for transplant. However, ASCT is not curative and patients relapse after a median interval of 24–30 months. While new therapeutic options have become available for relapsed MM, repeat ASCT remains an option especially when previously collected stem cells are available. The outcome of pts going to a second SCT in the relapsed setting has not been studied extensively. Methods: We identified pts with myeloma who received a second SCT from a prospectively maintained database. Planned tandem ASCTs were excluded. 56 pts received a second SCT for relapsed MM, including 11 allogeneic SCTs. Among the 45 second ASCTs, 5 were followed by reduced intensity allogeneic SCT and were analyzed with the allogeneic group. Results: The median age at second ASCT was 60.2 yrs (range, 41.3–74.4) and 27 (68%) were males. The median time to second ASCT from diagnosis, first ASCT and relapse were 47.4 mos (22.8–158.6), 36.3 mos (13.5–129.8) and 7.2 mos (1–32) respectively. Among patients receiving second APBSC, 14 (35%) patients were alive with a median follow up of 10.5 mos (1–45 mos). All patients received melphalan conditioning. The median time to neutrophil engraftment was 15 days and platelet engraftment was 16 days. The median hospitalization was 4 days (range 0–33) and there was one transplant related death in the group. The best response included 13 pts with CR (33%), 4 with VGPR (10%), and 19 with PR (48%). MM has relapsed in 22 (55%) pts with a median PFS of 12.5 mos from second ASCT. The median estimated OS from diagnosis, first ASCT and second ASCT were 100.5 mos, 65.9 mos, and 30.6 mos respectively. Among the 16 pts receiving allogeneic SCT, 8 pts (50%) were alive at analysis with a median PFS and OS from transplant of 17.9 mos and 33.5 mos respectively. Conclusions: Second ASCT as salvage therapy for relapsed MM is a viable approach and has a favorable outcome in this selected group of patients. The toxicity, engraftment kinetics, hospitalization and the response rates are comparable to patients undergoing initial ASCT. Allogeneic SCT with or with out a preceding ASCT results in comparable survival in selected patients with high risk disease.

No significant financial relationships to disclose.

Study of erythrocyte shape changes in schistosomiasis

The aim of this work was to study the red cell morphology in different stages of schistosomiasis. Patients were divided into three groups according to the stage of the disease. For each patient, complete clinical examination, liver function tests, renal function tests, complete blood picture, scanning electron microscopy for erythrocytes (SEM) and abdominal ultrasonography were done. Abnormal morphologic changes of a total discoid flat cells of 70.14%, margin changes of 12.34% and 3.55% of cup forms were found. To our knowledge, these marked changes were not reported in any other disease. No statistical differences were found between red cell shape changes and stage of liver disease. There was a positive correlation between portal vein diameter and percentage of flat discoid forms and a negative correlation between surface changes and clinical stage of liver disease. These changes are known to be accompanied by reduction of red cell deformability and impaired capillary flow.

Pleural effusion in complicated Salmonella paratyphi A infection

Enteric fever can present with unusual manifestations. We observed a rare case of Salmonella paratyphi A infection in which multiple organs were involved and the organism was isolated from pleural fluid and blood. In the present era of antimicrobial drug resistance, awareness about such atypical presentations is essential to initiate a prompt treatment.

Rhesus rhadinovirus infection in healthy and SIV-infected macaques at Tulane National Primate Research Center

Rhesus rhadinovirus (RRV) infection was quantified in peripheral blood mononuclear cells (PBMC) from healthy and simian immunodeficiency virus (SIV)-infected rhesus macaques (Macaca mulatta) at the Tulane National Primate Research Center and in a large collection of simian acquired immunodeficiency syndrome--(SAIDS)-associated lymphomas. Quantification of RRV load was performed by real-time PCR using amplification primers specific for the RRV interleukin-6 homologue (RRV vIL-6). RRV infection was detected infrequently and at low levels in PBMC of randomly selected healthy animals. Examination of longitudinally collected PBMC from 22 SIV-infected animals throughout progression to SAIDS revealed similarly low RRV loads that sometimes increased with advancing disease. RRV infection was detected more frequently in the peripheral blood of SIV-infected animals than in healthy animals. Examination of SAIDS-associated lymphomas showed that RRV is rare within the tumor mass, likely representing infection in an occasional tumor-infiltrating cell or contaminating blood. The results indicate that RRV infection in PBMC is not predictive of, and is apparently not required for, development of lymphoma or hyperplastic lymphadenopathy in SIV-infected animals at TNPRC.

Single vs weekly courses of antenatal corticosteroids for women at risk of preterm delivery: A randomized controlled trial

CONTEXT

The practice of administering weekly courses of antenatal corticosteroids to pregnant women at risk of preterm delivery is widespread, but no randomized trial has established the efficacy or safety of this practice.

OBJECTIVES

To evaluate the efficacy of weekly administration of antenatal corticosteroids compared with a single course in reducing the incidence of neonatal morbidity and to evaluate potential complications of weekly treatment.

DESIGN AND SETTING

Randomized, double-blind, placebo-controlled intention-to-treat trial conducted in 13 academic centers in the United States from February 1996 through April 2000.

PARTICIPANTS

A total of 502 pregnant women between 24 and 32 completed weeks' gestation who were at high risk of preterm delivery.

INTERVENTION

All patients received a complete single course of antenatal corticosteroids (either betamethasone, 12 mg intramuscularly repeated once in 24 hours for 2 doses, or dexamethasone, 6 mg intramuscularly repeated every 12 hours for 4 doses). Participants who had not delivered 1 week after receipt of the single course were randomly assigned to receive either betamethasone, 12 mg intramuscularly repeated once in 24 hours for 2 doses every week until 34 weeks' gestation or delivery, whichever came first (n = 256), or a similarly administered placebo (n = 246).

MAIN OUTCOME MEASURE

Composite neonatal morbidity (including severe respiratory distress syndrome, bronchopulmonary dysplasia, severe intraventricular hemorrhage, periventricular leukomalacia, proven sepsis, necrotizing enterocolitis, or perinatal death).

RESULTS

Composite morbidity occurred in 22.5% of the weekly-course group vs 28.0% of the single-course group (unadjusted relative risk, 0.80; 95% confidence interval, 0.59-1.10). Neither group assignment nor the number of treatment courses was associated with a reduction in composite morbidity.

CONCLUSIONS

Weekly courses of antenatal corticosteroids did not reduce composite neonatal morbidity compared with a single course of treatment. Weekly courses of antenatal corticosteroids should not be routinely prescribed for women at risk of preterm delivery.

Relationship between peripheral intravenous catheter Dwell time and the development of phlebitis and infiltration

The purpose of this study was to evaluate whether lengthening the dwell time of peripheral i.v. catheters from 72 hours to 144 hours resulted in increased rates of phlebitis and/or infiltration. The study was conducted in medical/surgical units at a 110-bed teaching hospital with an i.v. team. Kaplan-Meier estimates of the success and failure and conditional failure probabilities were calculated for phlebitis and infiltration scores. Log rank tests were used to test for an association between the covariates and the time until failure. Drug irritation was the most significant predictor of phlebitis and infiltration rates in this study. The total difference in the estimated failure rates for the catheter lasting 6 days versus a new catheter inserted for another 3 days is 1.3%. Because the conditional failure probability estimates for days 4, 5, and 6 are slightly higher than for days 1, 2, and 3, consideration may be given to extending the dwell time of a peripheral i.v. catheter beyond 72 hours under certain circumstances.

Guide RNAs of the recently isolated LEM125 strain of Leishmania tarentolae: an unexpected complexity

Guide RNAs (gRNAs) are encoded both in the maxicircle and minicircle components of the mitochondrial DNA of trypanosomatid protozoa. These RNAs mediate the precise insertion and deletion of U residues in transcripts of the maxicircle DNA. We showed previously that the old UC laboratory strain of Leishmania tarentolae apparently lost more than 40 minicircle-encoded gRNAs that are present in the recently isolated LEM125 strain (Thiemann et al., EMBO J, 1994, 13:5689-5700]. We have further analyzed the population of minicircle-encoded gRNAs in the LEM125 strain. Sau3AI and MspI minicircle libraries were constructed and screened for novel gRNAs by negative colony hybridization. This search yielded 20 minicircles encoding new gRNAs that covered most of the remaining gaps in the editing cascades of the ND8, ND9, G4, and G5 genes, and in addition, more than 30 minicircles containing either unassigned or undetectable gRNA genes. We also completely sequenced 34 of the 45 minicircle sequence classes encoding previously identified gRNAs. A total of 19 pairs of redundant gRNAs, which are gRNAs of different sequences covering the same editing blocks, were identified. The gRNAs in each redundant pair generally had different relative abundances and different extents of mismatches with edited sequences. Alignments of the minicircles encoding redundant gRNAs yielded 59 to 93% matching nucleotides, suggesting an origin from duplication of ancestral minicircles and subsequent genetic drift. We propose a functional explanation for the existence of redundant gRNAs in this strain.

Indwelling urethral catheters

Lesley Simpson discusses the risks associated with indwelling urethral catheters and identifies how nurses can reduce them with proactive management.

PTEN expression causes feedback upregulation of insulin receptor substrate 2

PTEN is a tumor suppressor that antagonizes phosphatidylinositol-3 kinase (PI3K) by dephosphorylating the D3 position of phosphatidylinositol (3,4,5)-triphosphate (PtdIns-3,4,5-P3). Given the importance of PTEN in regulating PtdIns-3,4,5-P3 levels, we used Affymetrix GeneChip arrays to identify genes regulated by PTEN. PTEN expression rapidly reduced the activity of Akt, which was followed by a G(1) arrest and eventually apoptosis. The gene encoding insulin receptor substrate 2 (IRS-2), a mediator of insulin signaling, was found to be the most induced gene at all time points. A PI3K-specific inhibitor, LY294002, also upregulated IRS-2, providing evidence that it was the suppression of the PI3K pathway that was responsible for the message upregulation. In addition, PTEN, LY294002, and rapamycin, an inhibitor of mammalian target of rapamycin, caused a reduction in the molecular weight of IRS-2 and an increase in the association of IRS-2 with PI3K. Apparently, PTEN inhibits a negative regulator of IRS-2 to upregulate the IRS-2-PI3K interaction. These studies suggest that PtdIns-3,4,5-P3 levels regulate the specific activity and amount of IRS-2 available for insulin signaling.

Isolation and characterization of a U-specific 3'-5'-exonuclease from mitochondria of Leishmania tarentolae

We have purified a 3'-5'-exoribonuclease from mitochondrial extract of Leishmania tarentolae over 4000-fold through six column fractionations. This enzyme digested RNA in a distributive manner, showed a high level of specificity for 3'-terminal Us, and was blocked by a terminal dU; there was slight exonucleolytic activity on a 3'-terminal A or C but no activity on a 3'-terminal G residue. The enzyme preferred single-stranded 3'-oligo(U) overhangs and did not digest duplex RNA. Two other 3'-5'-exoribonuclease activities were also detected in the mitochondrial extract, one of which was stimulated by a 3'-phosphate and the other of which degraded RNAs with a 3'-OH to mononucleotides in a processive manner. The properties of the distributive U-specific 3'-5'-exoribonuclease suggest an involvement in the U-deletion RNA editing reaction that occurs in the mitochondrion of these cells.

Promoting education, mentorship, and support for pediatric research

Pediatricians have an important role to play in the advancement of child health research and should be encouraged and supported to pursue research activities. Education and training in child health research should be part of every level of pediatric training. Continuing education and access to research advisors should be available to practitioners and academic faculty. Recommendations to promote additional research education and support at all levels of pediatric training, from premedical to continuing medical education, as well as suggestions for means to increase support and mentorship for research activities, are outlined in this statement.

PTEN: life as a tumor suppressor

PTEN, a tumor suppressor located at chromosome 10q23, is mutated in a variety of sporadic cancers and in two autosomal dominant hamartoma syndromes. PTEN is a phosphatase which dephosphorylates phosphatidylinositol (3,4,5)-triphosphate (PtdIns-3,4,5-P3), an important intracellular second messenger, lowering its level within the cell. By dephosphorylating PtdIns-3,4,5-P3, PTEN acts in opposition to phosphatidylinositol 3-kinase (PI3K), which has a pivotal role in the creation of PtdIns-3,4,5-P3. PtdIns-3,4,5-P3 is necessary for the activation of Akt, a serine/threonine kinase involved in cell growth and survival. By blocking the activation of Akt, PTEN regulates cellular processes such as cell cycling, translation, and apoptosis. In this review, we will discuss the identification of PTEN, its mutational status in cancer, its role as a regulator of PI3K, and its domain structure.

Low dependency residents in private nursing homes in Glasgow

OBJECTIVES

To investigate why nursing home care had been recommended for elderly people who were assessed subsequently as being of low dependency.

DESIGN

Examination of community care assessment documentation for low dependency residents to assess reasons for recommending nursing home care; comparison of these with data from a subsequent SCRUGs (Scottish Care Resource Utilisation Groups) assessment.

SETTING AND SUBJECTS

Three hundred and four residents within eight private nursing homes in Glasgow.

RESULTS

Twenty six percent of the residents were described as being of low dependency. Of these, 44% had dementia and 6% personal care needs alone; 29% had medical problems which required nursing input, but not necessarily to a level requiring nursing home care. Information in the community care assessment often described a higher level of need than that identified subsequently. From the information given in the medical component of the community care assessment it was often unclear why the decision to recommend nursing home care was made.

CONCLUSION

Admission to nursing homes may be encouraged by over-emphasiZing care requirements, by placing emphasis on safety rather than independence and by inadequate recording of information. Elderly people who cannot remain at home need improved assessment procedures, better understanding of their needs and a wider range of accommodation options.

Pediatric environmental health: perceptions from a survey questionnaire

To expand the base of knowledge regarding perceptions about potential environmental threats to children's health, a survey was conducted in the Northwest United States. Samples of Head Start parents, PTA presidents, public health officials, school nurses, naturopathic physicians, family practitioners, and pediatricians were mailed a questionnaire inquiring into the nature and degree of concerns about pediatric environmental health. The response rate was 24%. Trends in the data showed disparities in perceptions regarding levels of concern and exposure concerns between respondent categories. Disparities also existed regarding information resources used for children's environmental health. Recognizing differences in perceptions of children's environmental health, as demonstrated in these results, may be useful for risk communication and resource allocation, especially in the context of the wide variety of health belief models. Such knowledge may help clarity situations with environmental health risk concerns, including clinical, public health, and educational circumstances.

Annual report on access to and utilization of health care for children and youth in the United States--2000

OBJECTIVE

This report provides an update on insurance coverage, use of health care services, and health expenditures for children and youth in the United States. In addition, the report provides information on variation in hospitalizations for children from a new 22-state hospital discharge data source.

METHODS

The data on insurance coverage, utilization, and expenditures come from the Medical Expenditure Panel Survey. The data on hospitalizations come from the Database for Pediatric Studies, which is part of the Healthcare Cost and Utilization Project. Both data sets have been prepared by the Agency for Healthcare Research and Quality.

RESULTS

Few changes in insurance coverage occurred between 1996 and 1998. About two thirds of American children are covered by private insurance and 19% by public sources; the remaining 15% are uninsured. Of the 71.5% of children who have at least 1 doctor's office visit, the average number of visits was 3.9, but this ranged from 2.7 among the uninsured to 4.2 for those with private insurance. Slightly more than half of children had a prescription, and these averaged 5.4 prescriptions. The majority of children (85%) incur medical expenditures, averaging $1019 for children with any expenditure. Private health insurance was by far the largest payer of medical care expenses for children, even more so than among the general population. However, nearly 21% of expenditures for children's health care were paid out of pocket by children's families. The data also show substantial differences in average length of hospitalization across states, ranging from 2.7 to 4.0 days, and rates of hospital admission through the emergency department, which vary across states from 9% to 23%. Injuries are a major reason for hospitalization, accounting for 1 in 6 hospital stays among 10- to 14-year-olds. In the 10-17 age group, 1 in 7 hospital stays are due to mental disorders. Among 15- to 17-year-olds, more than one third of all hospital stays are related to childbirth and pregnancy.

CONCLUSION

Children's use of health care services varies considerably by what type of health insurance coverage they have. Expenditures for children entail a substantial out-of-pocket component, which may be quite large for children with major health problems and which may represent a significant burden on lower-income families. Substantial variation in hospitalization exits across states.

End processing precedes mitochondrial importation and editing of tRNAs in Leishmania tarentolae

All mitochondrial tRNAs in Leishmania tarentolae are encoded in the nuclear genome and imported into the mitochondrion from the cytosol. One imported tRNA (tRNA(Trp)) is edited by a C to U modification at the first position of the anticodon. To determine the in vivo substrates for mitochondrial tRNA importation as well as tRNA editing, we examined the subcellular localization and extent of 5'- and 3'-end maturation of tRNA(Trp)(CCA), tRNA(Ile)(UAU), tRNA(Gln)(CUG), tRNA(Lys)(UUU), and tRNA(Val)(CAC). Nuclear, cytosolic, and mitochondrial fractions were obtained with little cross-contamination, as determined by Northern analysis of specific marker RNAs. tRNA(Gln) was mainly cytosolic in localization; tRNA(Ile) and tRNA(Lys) were mainly mitochondrial; and tRNA(Trp) and tRNA(Val) were shared between the two compartments. 5'- and 3'-extended precursors of all five tRNAs were present only in the nuclear fraction, suggesting that the mature tRNAs represent the in vivo substrates for importation into the mitochondrion. Consistent with this model, T7-transcribed mature tRNA(Ile) underwent importation in vitro into isolated mitochondria more efficiently than 5'-extended precursor tRNA(Ile). 5'-Extended precursor tRNA(Trp) was found to be unedited, which is consistent with a mitochondrial localization of this editing reaction. T7-transcribed unedited tRNA(Trp) was imported in vitro more efficiently than edited tRNA(Trp), suggesting the presence of importation determinants in the anticodon.

Effect of mycobacterial infection on virus loads and disease progression in simian immunodeficiency virus-infected rhesus monkeys

The effect of a mycobacterial infection on AIDS disease was studied in the simian model. Monkeys were infected with the primary virulent isolate SIV/DeltaB670 and inoculated 90 days later with BCG, an attenuated strain of Mycobacterium bovis. All monkeys experienced a dramatic transient increase in plasma viremia and CCR5 expression on T lymphocytes after BCG inoculation. Only two of the four SIV+ animals had substantial proliferative responses to PPD, with poor responders developing disseminated BCG during the course of the experiment. BCG inoculation of SIV-infected long-term nonprogressor (LTNP) monkeys was also performed. Similar to the acutely infected animals, two of three LTNPs experienced increases in plasma viral levels and CCR5 expression. In the majority of animals studied, there was no accelerated progression to AIDS despite the concomitant transient stimulation of virus replication and CCR5 expression on T lymphocytes.

What's half a lung worth? Civil jurors' accounts of their award decision making

Jury awards are often criticized as being arbitrary and excessive. This paper speaks to that controversy, reporting data from interviews with civil jurors' accounts of the strategies that juries use and the factors that they consider in arriving at a collective award. Jurors reported difficulty in deciding on awards, describing it as "the hardest part" of jury service and were surprised the court did not provide more guidance to them. Relatively few jurors entered the jury deliberation room with a specific award figure in mind. Once in the deliberation room, however, they reported discussing a variety of relevant factors such as the seriousness of the injury, the plaintiff's age, and occasionally even more esoteric items such as the impact of inflation. Two frequent topics of discussion, attorneys' fees and insurance, suggest that jurors attempt to estimate the actual impact of an award on both defendant and plaintiff. This descriptive account may help to inform the debate about whether jurors require additional guidance or information in the award process.

Selective importation of RNA into isolated mitochondria from Leishmania tarentolae

All mitochondrial tRNAs in kinetoplastid protozoa are encoded in the nucleus and imported from the cytosol. Incubation of two in vitro-transcribed tRNAs, tRNA(Ile)(UAU) and tRNA(Gln)(CUG), with isolated mitochondria from Leishmania tarentolae, in the absence of any added cytosolic fraction, resulted in a protease-sensitive, ATP-dependent importation, as measured by nuclease protection. Evidence that nuclease protection represents importation was obtained by the finding that Bacillus subtilis pre-tRNA(Asp) was protected from nuclease digestion and was also cleaved by an intramitochondrial RNase P-like activity to produce the mature tRNA. The presence of a membrane potential is not required for in vitro importation. A variety of small synthetic RNAs were also found to be efficiently imported in vitro. The data suggest that there is a structural requirement for importation of RNAs greater than approximately 17 nt, and that smaller RNAs are apparently nonspecifically imported. The signals for importation of folded RNAs have not been determined, but the specificity of the process was illustrated by the higher saturation level of importation of the mainly mitochondria-localized tRNA(Ile) as compared to the level of importation of the mainly cytosol-localized tRNA(Gln). Furthermore, exchanging the D-arm between the tRNA(Ile) and the tRNA(Gln) resulted in a reversal of the in vitro importation behavior and this could also be interpreted in terms of tertiary structure specificity.

Evolution of RNA editing in trypanosome mitochondria

Two different RNA editing systems have been described in the kinetoplast-mitochondrion of trypanosomatid protists. The first involves the precise insertion and deletion of U residues mostly within the coding regions of maxicircle-encoded mRNAs to produce open reading frames. This editing is mediated by short overlapping complementary guide RNAs encoded in both the maxicircle and the minicircle molecules and involves a series of enzymatic cleavage-ligation steps. The second editing system is a C(34) to U(34) modification in the anticodon of the imported tRNA(Trp), thereby permitting the decoding of the UGA stop codon as tryptophan. U-insertion editing probably originated in an ancestor of the kinetoplastid lineage and appears to have evolved in some cases by the replacement of the original pan-edited cryptogene with a partially edited cDNA. The driving force for the evolutionary fixation of these retroposition events was postulated to be the stochastic loss of entire minicircle sequence classes and their encoded guide RNAs upon segregation of the single kinetoplast DNA network into daughter cells at cell division. A large plasticity in the relative abundance of minicircle sequence classes has been observed during cell culture in the laboratory. Computer simulations provide theoretical evidence for this plasticity if a random distribution and segregation model of minicircles is assumed. The possible evolutionary relationship of the C to U and U-insertion editing systems is discussed.

Stress incontinence in younger women: prevention and treatment

Urinary stress incontinence is prevalent in older people, but it has also been found to affect fit nulliparous women. Building pelvic floor muscles with pelvic muscle exercises helps to treat stress incontinence in women, but if exercises are begun at an early age, it is also effective in reducing the incidence of stress incontinence later in life.

Rhesus lymphocryptovirus infection during the progression of SAIDS and SAIDS-associated lymphoma in the rhesus macaque

SAIDS-associated lymphoma (SAL) represents a monoclonal expansion of B-cell origin in which simian immunodeficiency virus (SIV) infection is not detected. However, tumor cells are frequently infected with rhesus lymphocryptovirus (RhLCV), a rhesus homologue of Epstein-Barr virus (EBV). In previous studies, the incidence of RhLCV infection in SAL was determined to be 89% as measured by polymerase chain reaction (PCR) and/or in situ hybridization. The main objective of the present study was to ascertain whether the level of RhLCV infection in the SIV-infected macaque is influenced as a function of SAIDS progression, and/or whether increased levels of RhLCV infection may correlate with the development of SAL. To this end, RhLCV infection was evaluated in three independent groups: (1) in lymphomas from SIV-infected rhesus macaques, (2) in peripheral blood mononuclear cells (PBMC) from a cohort of 69 randomly selected healthy animals, and (3) in PBMC collected from 22 SIV-infected animals at various times during progression to SAIDS or SAL. The relative levels of RhLCV infection were evaluated by PCR/Southern blot analysis, visual comparison to a standard dilution series, and assignment of relative signal intensity to a uniform classification scheme. The data show that SIV-infected monkeys have a generally higher RhLCV load in PBMC than do healthy animals, but that the virus load varies widely among animals during disease progression. Increased RhLCV load does not occur uniformly during the progression of SAIDS, although evidence indicates an increased RhLCV viral load in the development of SAL.

C to U editing of the anticodon of imported mitochondrial tRNA(Trp) allows decoding of the UGA stop codon in Leishmania tarentolae

All mitochondrial tRNAs in kinetoplastid protists are encoded in the nucleus and imported into the organelle. The tRNA(Trp)(CCA) can decode the standard UGG tryptophan codon but can not decode the mitochondrial UGA tryptophan codon. We show that the mitochondrial tRNA(Trp) undergoes a specific C to U nucleotide modification in the first position of the anticodon, which allows decoding of mitochondrial UGA codons as tryptophan. Functional evidence for the absence of a UGA suppressor tRNA in the cytosol, using a reporter gene, was also obtained, which is consistent with a mitochondrial localization of this editing event. Leishmania cells have dealt with the problem of a lack of expression within the organelle of this non-universal tRNA by compartmentalizing an editing activity that modifies the anticodon of the imported tRNA.

Uridine insertion/deletion RNA editing in trypanosome mitochondria--a review

The uridine insertion/deletion RNA editing in trypanosome mitochondria is a unique posttranscriptional RNA maturation process that involves the addition or removal of uridine residues at precise sites usually within the coding regions of mitochondrial transcripts. This process creates initiation and termination codons, corrects frameshifts and even builds entire open-reading frames from nonsense sequences. The development of several in-vitro editing assays has provided much insight into the molecular mechanism of RNA editing, which appears to involve cleavage, U addition, exonuclease trimming and ligation, essentially as proposed in the original 'enzyme cascade' model (Blum, B., Bakalara, N., Simpson, L., 1990. A model for RNA editing in kinetoplastid mitochondria: 'Guide' RNA molecules transcribed from maxicircle DNA provide the edited information. Cell 60, 189-198). However, little is known about the biochemical properties of the proteins involved and the significance and role of this process. This article is a review of recent findings on uridine-insertion/deletion editing in trypanosome mitochondria, with an emphasis on the proteins isolated and characterized that may have a role in this process.

T7 RNA polymerase-driven transcription in mitochondria of Leishmania tarentolae and Trypanosoma brucei

The study of RNA editing and other molecular processes in the trypanosome mitochondrion would benefit greatly from the ability to insert and express exogenous DNA in the organelle. However, even with a method to introduce DNA, the current lack of knowledge about mitochondrial transcription would hinder efforts to obtain expression. To circumvent this problem, Leishmania tarentolae promastigotes and Trypanosoma brucei procyclic cells have been transfected with bacteriophage T7 RNA polymerase targeted to the mitochondrion. Mitochondria isolated from the transfectants contained active T7 RNA polymerase, as shown by a comigration in density gradients of mitochondrial marker enzymes and T7 polymerase activity. A DNA cassette under T7 control was introduced into isolated mitochondria from the transfectants by electroporation and the DNA was shown to be transcribed. This system should allow the transcription of foreign genes of choice within the mitochondrial matrix either in a transient assay using electroporation of DNA into isolated mitochondria, or in a stable assay using cells transfected with DNA by the biolistic gun method.