An evolutionarily conserved RNA stem-loop functions as a sensor that directs feedback regulation of RNase E gene expression

RNase E is a key regulatory enzyme that controls the principal pathway for mRNA degradation in Escherichia coli. The cellular concentration of this endonuclease is governed by a feedback mechanism in which RNase E tightly regulates its own synthesis. Autoregulation is mediated in cis by the 361-nucleotide 5' untranslated region (UTR) of rne (RNase E) mRNA. Here we report the determination of the secondary structure of the rne 5' UTR by phylogenetic comparison and chemical alkylation, together with dissection studies to identify the 5' UTR element that mediates autoregulation. Our findings reveal that the structure and function of the rne 5' UTRs are evolutionarily well conserved despite extensive sequence divergence. Within the rne 5' UTRs are multiple RNA secondary structure elements, two of which function in cis to mediate feedback regulation of rne gene expression. The more potent of these two elements is a stem-loop structure containing an internal loop whose sequence is the most highly conserved of any region of the rne 5' UTR. Our data show that this stem-loop functions as a sensor of cellular RNase E activity that directs autoregulation by modulating the degradation rate of rne mRNA in response to changes in RNase E activity.

RNA recognition by the joint action of two nucleolin RNA-binding domains: genetic analysis and structural modeling

The interaction of nucleolin with a short stem-loop structure (NRE) requires two contiguous RNA-binding domains (RBD 1+2). The structural basis for RNA recognition by these RBDs was studied using a genetic system in Escherichia coli. Within each of the two domains, we identified several mutations that severely impair interaction with the RNA target. Mutations that alter RNA-binding specificity were also isolated, suggesting the identity of specific contacts between RBD 1+2 amino acids and nucleotides within the NRE stem-loop. Our data indicate that both RBDs participate in a joint interaction with the NRE and that each domain uses a different surface to contact the RNA. The constraints provided by these genetic data and previous mutational studies have enabled us to propose a three-dimensional model of nucleolin RBD 1+2 bound to the NRE stem-loop.

Models for pairing of IS10 encoded antisense RNAs in vivo

Antisense regulation of IS10 transposase synthesis is mediated by a small RNA molecule, RNA-OUT which is complementary to the 5' region of the IS10 transposase mRNA, RNA-IN. Pairing between the two species in vivo prevents initiation of RNA-IN translation by steric occlusion of the ribosome binding site. The goal of this work is to develop a mathematical basis for antisense repression in vivo. Thus, by modeling antisense pairing as a biomolecular reaction in vivo, I have developed equations which relate the degree of translation inhibition to a relative pairing rate constant, k, and the in vivo RNA-OUT concentration. Using the methodology developed here, an analysis of mutations in the first three 5' bases of RNA-IN reveals a semi-logarithmic relationship between k and delta G, the estimated change in the free energy of pairing. Such correlations are not observed for mutations at other positions, implicating only the first three 5' bases of RNA-IN in the formation of a pairing nucleus with RNA-OUT. Finally, an analysis of mutations that affect antisense action at a post-nucleation step has been undertaken here and a specific model for how these mutations may affect antisense pairing is discussed.

A structural model for the HIV-1 Rev-RRE complex deduced from altered-specificity rev variants isolated by a rapid genetic strategy

A broadly applicable genetic strategy was developed for investigating RNA-protein interactions and applied to the HIV-1 Rev protein. By rapidly screening thousands of Rev-RNA interactions in Escherichia coli, we isolated Rev suppressor mutations that alleviated the deleterious effect of mutations in RRE stem-loop IIB, the high affinity RNA-binding site for Rev. All of these suppressor mutations map to a single arginine-deficient face of a Rev alpha-helix, and some alter the binding specificity of the protein, providing genetic evidence for direct contacts between specific Rev amino acids and RNA nucleotides in the RNA complex of Rev. The spatial constraints suggested by these data have enabled us to model the structure of this complex.

Atypical manifestations of tinea faciei

A study of 58 paitents of tinea faciei was conducted. Twenty five (43.1%) patients had history of photosensitivity. Twenty eight (48.2%) patients were applying topical steroids, 2 (3.4%) patients were on 10 mg of prednisolone daily. Associated tinea of other sites were observed in 14 (24.13%). 23 (39.6%) patients had typical circinate, arcuate, annular plaques with raised margin showing vesiculo-pustules. Atypical manifestations were in the form of arcuate plaques on the pinna in 4 patients, erythematous plaques full of vesiculo-pustules without central clearing in 3. Thirty two (55.17%) patients had plaques with broad edges and indistinct central clearing. In 2 patients lesions resembled discoid lupus erythematosus. Skin scrapings for fungus was positive in 36 (62.06%) cases. All patients responded to systemic griseofulvin 10mg/kg with 1% clotrimazole topicaly in 4-8 weeks.

Unusual clinical and histopathological presentation of facial tuberculosis

Atypical facial lupus vulgaris is described in two cases. The first case resembled sarcoidosis clinically and histologically but responded well to ATT. The second case whose clinical diagnosis of lupus vulgaris was confirmed therapeutically had an atypical histology.

Preparation and characterization of niosomes containing rifampicin for lung targeting

Niosomes (non-ionic, surfactant-based vesicles) containing rifampicin of 8-15 microns in diameter were prepared using Span-85 and cholesterol in various molar fractions. The process variables that could affect the physical characteristics of niosomes and in vitro release of the drug from the niosomes were studied and optimized. In vivo distribution studies of the prepared niosomes found that 65% of the drug could be localized in the lungs by controlling the niosome size.

IS10 antisense control in vivo is affected by mutations throughout the region of complementarity between the interacting RNAs

Translation of the IS10 transposase mRNA (RNA-IN) is inhibited by antisense pairing with a small IS10 encoded transcript called RNA-OUT. To further characterize IS10 antisense control, an extensive set of mutations in the region of complementarity between RNA-OUT, and its target RNA-IN have been isolated. These mutations have been characterized for their effects on antisense inhibition of transposase gene translation in vivo. Mutations that confer the strongest defects on translational inhibition are found in the region corresponding to the 5' end of RNA-IN. However, mutations throughout the complementary region affect antisense control regardless of whether mutations are present in RNA-IN alone or as complementary mutations in both RNAs. An analysis of the data presented here suggests that in vivo pairing rates for the wild-type antisense species are very close to being optimal. Some of the motifs found in antisense molecules that may be associated with efficient pairing rates are discussed.

Drug-induced pseudolymphoma syndrome

Five cases of pseudolymphoma syndrome (PS) in children aged six to twelve years were observed after anticonvulsant drugs. In two cases PS was observed after ten days and in three after fifteen days of therapy with the offending drug. Three cases of PS were due to carbamazepine and had morbilliform rash and two cases due to phenobarbitone had erythroderma. All had fever, generalised lymphadenopathy and 4/5 had hepatosplenomegaly. Therapy with 15 mg prednisolone daily and withdrawal of the offending durg led to cure in 4/5 cases and one died due to congestive cardiac failure.

Autoregulation of RNase E synthesis in Escherichia coli

RNase E plays a central role in controlling mRNA degradation in E. coli. We have investigated the mechanism of RNase E autoregulation. Our data indicate that RNase E autoregulates its synthesis by controlling the decay rate of its own transcript (rne mRNA), which is unusually sensitive to the level of cellular RNase E activity. Feedback regulation is mediated in cis by the rne 5' untranslated region (5' UTR), which can confer this property onto heterologous mRNAs to which it is fused. The marked sensitivity of rne mRNA to regulation by RNase E is also due in part to the susceptibility of nascent rne transcripts to RNase E-mediated degradation.

Recurrent herpes zoster in a child with SLE

A 12-year-old girl had systemic lupus erythematosus (SLE) and type IV lupus nephritis since three-and-a-half years. She was treated with prednisolone and cyclophosphamide. She had first attack of herpes zoster (HZ) involving eighth and ninth thoracic segments on right side at the age of nine years. Second attack occurred on the same segments on same side at the age of twelve years. The second attack of herpes zoster was treated with oral acyclovir 400 mg five times a day for seven days plus analgesics and multi-vitamins. Most probably this is the first case of recurrent herpes zoster (RHZ) in a child in Indian literature.

RNase E autoregulates its synthesis by controlling the degradation rate of its own mRNA in Escherichia coli: unusual sensitivity of the rne transcript to RNase E activity

RNase E is a key regulatory enzyme that appears to control the principal pathway for mRNA degradation in Escherichia coli. Here, we show that RNase E represses its own synthesis by reducing the cellular concentration of the rne (RNase E) gene transcript. Autoregulation is achieved by modulating the longevity of this 3.6-kb mRNA, whose half-life ranges from < 40 sec to > 8 min depending on the level of RNase E activity in the cell. Feedback regulation is mediated in cis by the 5'-terminal 0.44-kb segment of rne mRNA, which is sufficient to confer this property onto a heterologous transcript to which it is fused. Like the intact protein, an amino-terminal fragment of RNase E lacking 563 amino acid residues can act in trans to repress rne gene expression. Paradoxically, raising the rne gene copy number 21-fold in E. coli causes an unexpected reduction in the concentration of the full-length rne transcript, yet results in a small increase in RNase E protein production. These surprising phenomena are explained in terms of a model in which the degradation of this long and highly labile mRNA commences before elongation of the nascent transcript has been completed. In such circumstances, gene expression can be unusually sensitive to changes in mRNA stability.

New improved lacZ gene fusion vectors

New plasmid vectors suitable for creating fusions with the lacZ gene have been developed. These vectors represent an improvement over currently available vectors and possess the following features: (1) an undetectable background beta-galactosidase (beta Gal) activity in the absence of fusion, (2) an extended multiple cloning site (MCS), and (3) the ability to conveniently subclone in any one of three translational frames. Medium- and high-copy-number versions of these vectors have been developed.

Preferential cis action of IS10 transposase depends upon its mode of synthesis

A number of bacterial DNA-binding proteins, including IS element transposases, act preferentially in cis. We show below that the degree of preferential cis action by IS10 transposase depends upon its mode of synthesis at steps subsequent to transcription initiation. Cis preference is increased several fold by mutations that decrease translation initiation, by the presence of IS10-specific antisense RNA and by plasmids that increase the level of cellular RNases. Conversely, cis preference is decreased by mutations that increase translation initiation; in some cases, cis preference is nearly abolished. Mutations that alter the rate of transcription initiation have no effect. In light of other observations, we suggest that cis preference is strongly dependent upon the rate at which transcripts are released from their templates and/or the half-life of the transposase message. These observations provide further evidence that inefficient translation plays multiple roles in the biology of IS10.

IS10 mRNA stability and steady state levels in Escherichia coli: indirect effects of translation and role of rne function

Translation of the IS10 transposase gene is known to be very infrequent. We have identified mutations whose genetic properties suggest that they act directly to increase or decrease the intrinsic level of translation initiation. Also, we have analysed in detail the effects of these mutations on IS10 mRNA using one particular IS10 derivative. In this case, increases or decreases in translation are accompanied by increases or decreases in both the steady state level and the half-life of transposase mRNA; effects on steady state levels are much more dramatic than effects on message half-life. At wild-type levels of translation initiation, the rate-limiting step in physical decay of full length IS10 message for a particular IS10 derivative is shown to be rne-dependent endonucleolytic cleavage; 3' exonucleases appear to play a secondary role, degrading primary cleavage products. Analysis of interplay between translation mutations and rne function, together with the above observations, suggests that translation stabilizes messages in a general way against rne-dependent endonucleolytic cleavage, and that significant protection may be conferred by one or a few ribosomes. However, dramatic effects of translation on steady state message levels are still observed in an rne mutant and involve the 3' end of the transcript; we propose that these additional effects reflect translation-mediated stimulation of transcript release.

Bioadhesive polymer-grafted starch microspheres bearing isosorbide dinitrate for buccal administration

A polymer-grafted mucoadhesive system bearing isosorbide dinitrate was prepared for buccal administration. Polymer grafting of starch microspheres modified drug release and surface characteristics of microspheres. Bioadhesion and factors affecting bioadhesion were studied. Process variables that could affect microsphere size, and as a result the release of the drug, were also studied. It was observed that compression of grafted starch microspheres modified drug release and extended drug action via slow release following buccal application. Prepared system(s) were characterized for drug release and in vivo performance and compared with conventional oral treatment. The systems were noted to be promising.

Polymeric pseudolatices bearing pilocarpine for controlled ocular delivery

The pseudolatex-based ocular formulations of pilocarpine were prepared using different combinations of Eudragit RS 100 and polyvinyl pyrrolidone for prolonged and controlled release of the drug. The designed system was essentially based on polymeric pseudolatex dispersion. The process variables that effect the latex particle size, drug loading and release profiles of drug were studied. Preparations were evaluated for their in vitro performance with regard to release profile and diffusion co-efficient. The designed system exhibited linear relationship between cumulative drug release (Q) and square root of time (t0.5). The products selected on the basis of in vitro characterization were studied for in vivo performance evaluation. It was observed that the preparations exhibited in vivo prolonged therapeutic efficacy. Thus polymer based pseudolatices hold promise for controlled pilocarpine ocular delivery.