Outcome data from the LEAP (Live, Eat and Play) trial: a randomized controlled trial of a primary care intervention for childhood overweight/mild obesity

OBJECTIVES

To reduce gain in body mass index (BMI) in overweight/mildly obese children in the primary care setting.

DESIGN

Randomized controlled trial (RCT) nested within a baseline cross-sectional BMI survey.

SETTING

Twenty nine general practices, Melbourne, Australia.

PARTICIPANTS

(1) BMI survey: 2112 children visiting their general practitioner (GP) April-December 2002; (2) RCT: individually randomized overweight/mildly obese (BMI z-score <3.0) children aged 5 years 0 months-9 years 11 months (82 intervention, 81 control).

INTERVENTION

Four standard GP consultations over 12 weeks, targeting change in nutrition, physical activity and sedentary behaviour, supported by purpose-designed family materials.

MAIN OUTCOME MEASURES

Primary: BMI at 9 and 15 months post-randomization. Secondary: Parent-reported child nutrition, physical activity and health status; child-reported health status, body satisfaction and appearance/self-worth.

RESULTS

Attrition was 10%. The adjusted mean difference (intervention-control) in BMI was -0.2 kg/m(2) (95% CI: -0.6 to 0.1; P=0.25) at 9 months and -0.0 kg/m(2) (95% CI: -0.5 to 0.5; P=1.00) at 15 months. There was a relative improvement in nutrition scores in the intervention arm at both 9 and 15 months. There was weak evidence of an increase in daily physical activity in the intervention arm. Health status and body image were similar in the trial arms.

CONCLUSIONS

This intervention did not result in a sustained BMI reduction, despite the improvement in parent-reported nutrition. Brief individualized solution-focused approaches may not be an effective approach to childhood overweight. Alternatively, this intervention may not have been intensive enough or the GP training may have been insufficient; however, increasing either would have significant cost and resource implications at a population level.

Impaired neurovascular coupling by transhemispheric diaschisis in rat cerebral cortex

In acute brain disorders, elimination of the excitatory output from an injured brain region reduces activity in connecting brain regions remote from the lesion site (i.e., diaschisis). The authors examined the effect of functional ablation of the left cerebral cortex by cortical spreading depression (CSD) or topical application of tetrodotoxin on single cell spiking activity, baseline CBF, and neurovascular coupling in the right rat sensory cortex. CSD or tetrodotoxin in left cortex reduced the right cortical spontaneous spike rate by 36% and 45%, respectively. Baseline CBF in the right cortex was unaffected by a left-sided CSD, but decreased by 12% for left cortical application of tetrodotoxin. This suggested dissociation between spontaneous spiking activity and basal CBF. Left in-fraorbital nerve stimulation evoked local field potentials in right cerebral cortex that were reduced in amplitude by 19% for left CSD and by 23% for left tetrodotoxin application. The corresponding declines in the evoked CBF responses were 42% for CSD and 23% for tetrodotoxin. Vascular reactivity to adenosine remained unchanged in right cortex. Thus, transhemispheric diaschisis produced a pronounced decrease in the spontaneous spike rate accompanied by no reduction or a small reduction in basal CBF, and an attenuation in amplitudes of evoked synaptic responses and corresponding rises in CBF. The findings suggest that disturbed neurovascular coupling may contribute to the disturbance in brain function in acute transhemispheric diaschisis.

Context sensitivity of activity-dependent increases in cerebral blood flow

Functional neuroimaging in humans is used widely to study brain function in relation to human disease and cognition. The neural basis of neuroimaging signals is probably synaptic activity, but the effect of context, defined as the interaction between synaptic inhibition, excitation, and the electroresponsive properties of the targeted neurons, is not well understood. We examined here the effect of interaction of synaptic excitation and net inhibition on the relationship between electrical activity and vascular signals in the cerebellar cortex. We show that stimulation of the net inhibitory parallel fibers simultaneously with stimulation of the excitatory climbing fibers leads to a further rise in total local field potentials (LFP) and cerebral blood flow (CBF) amplitudes, not a decrease, as predicted from theoretical studies. However, the combined stimulation of the parallel and climbing fiber systems produced changes in CBF and LFP that were smaller than their algebraic sum evoked by separate stimulation of either system. This finding was independent of the starting condition, i.e., whether inhibition was superimposed on a state of excitation or vice versa. The attenuation of the increases in LFP and CBF amplitudes was similar, suggesting that synaptic activity and CBF were coupled under these conditions. The result might be explained by a relative neuronal refractoriness that relates to the intrinsic membrane properties of Purkinje cells, which determine the recovery time of these cells. Our work implies that neuronal and vascular signals are context-sensitive and that their amplitudes are modulated by the electroresponsive properties of the targeted neurons.

Neuronal deactivation explains decreased cerebellar blood flow in response to focal cerebral ischemia or suppressed neocortical function

Functional neuroimaging in humans with acute brain damage often reveals decreases in blood flow and metabolism in areas unaffected by the lesion. This phenomenon, termed diaschisis, is presumably caused by disruption of afferent excitatory input from the lesioned area to other brain regions. By characterizing its neurophysiological basis, we used cerebellar diaschisis to study the relationship between electrical activity and blood flow during decreased neuronal activity. Here we show that focal cerebral ischemia in rats causes diaschisis in the cerebellar cortex characterized by pronounced decreases in Purkinje cell spiking activity and small decreases in cerebellar blood flow. The findings were explained by decreased excitatory input to the cerebellar cortex, i.e., deactivation, as cerebellar neuronal excitability and vascular reactivity were preserved. Functional ablation of the cerebral cortex by either spreading depression or tetrodotoxin reproduced the changes in cerebellar function with complete recovery of Purkinje cell activity and cerebellar blood flow concomitant with recovery of neocortical function. Decreases of activity involving the contralateral frontal cortex produced the largest decrease in cerebellar electrical activity and blood flow. Our data suggest that deactivation explains the decreases in blood flow and metabolism in cerebellar diaschisis observed in human neuroimaging studies. Decreases in spiking activity were 3-7 times larger than the respective decreases in flow. Therefore, under pathological conditions, neuroimaging methods based on hemodynamic signals may only show small changes, although the underlying decrease in neuronal activity is much larger.

Systematic review of randomised controlled trials of sildenafil (Viagra) in the treatment of male erectile dysfunction

BACKGROUND

Sildenafil (Viagra), a new oral drug for the treatment of erectile dysfunction, was licensed for use across Europe in 1998.

AIM

To examine the effectiveness and safety of sildenafil as an oral treatment for erectile dysfunction.

DESIGN OF STUDY

Systematic review and meta-analysis.

SETTING

All published or unpublished randomised controlled trials comparing sildenafil with a placebo or alternative therapies.

METHOD

Published studies were sought by computerised searches of electronic databases using the keywords 'sildenafil' and 'Viagra'. A hand search was also done of the British Medical Journal, Lancet, Journal of the American Medical Association, New England Journal of Medicine, British journal of General Practice, Drug, Inpharma and Scrip. An assessment of quality of all identified studies and data extraction was undertaken independently by two researchers. Results were combined in a meta-analysis where appropriate, using RevMan version 3.

RESULTS

Twenty-one trials were identified. All trials showed a statistically significant improvement in erectile or sexual function in patients using sildenafil compared with a placebo. A meta-analysis of 16 trials reporting a global efficacy response showed that men were 3.57 (95% CI = 2.93-4.43) times as likely to have improved erections on sildenafil compared with those on a placebo. The number needed to treat to have one man with improved erections was two. The drug has a relatively safe side-effect profile.

CONCLUSIONS

Available research shows that sildenafil is an effective treatment for male erectile dysfunction. Many trial participants had some baseline erectile function and it is probable that in clinical practice, where the erectile function tends to be more impaired, the number needed to treat may be higher.

No Evidence for Early Decrease in Blood Oxygenation in Rat Whisker Cortex in Response to Functional Activation

Using optical methods through a closed cranial window over the rat primary sensory cortex in chloralose/urethane-anesthetized rats we evaluated the time course of oxygen delivery and consumption in response to a physiological stimulus (whisker deflection). Independent methodological approaches (optical imaging spectroscopy, single fiber spectroscopy, oxygen-dependent phosphorescence quenching) were applied to different modes of whisker deflection (single whisker, full whisker pad). Spectroscopic data were evaluated using different algorithms (constant pathlength, differential pathlength correction). We found that whisker deflection is accompanied by a significant increase of oxygenated hemoglobin (oxy-Hb), followed by an undershoot. An early increase in deoxygenated hemoglobin (deoxy-Hb) proceeded hyperoxygenation when spectroscopic data were analyzed by constant pathlength analysis. However, correcting for the wavelength dependence of photon pathlength in brain tissue (differential pathlength correction) completely eliminated the increase in deoxy-Hb. Oxygen-dependent phosphorescence quenching did not reproducibly detect early deoxygenation. Together with recent fMRI data, our results argue against significant early deoxygenation as a universal phenomenon in functionally activated mammalian brain. Interpreted with a diffusion-limited model of oxygen delivery to brain tissue our results are compatible with coupling between neuronal activity and cerebral blood flow throughout stimulation, as postulated 110 years ago by C. Roy and C. Sherrington (1890, J. Physiol. 11:85--108).

The effectiveness of the levonorgestrel-releasing intrauterine system in menorrhagia: a systematic review

OBJECTIVE

To determine whether the levonorgestrel-releasing intrauterine device (LNG-IUS), licensed at present for contraceptive use, may reduce menstrual blood loss with few side effects. If effective, surgery could be avoided with consequent resource savings.

METHODS

A systematic review addressing the effectiveness and cost effectiveness of the LNG-IUS for menorrhagia was undertaken.

RESULTS

Five controlled trials and five case series were found which measured menstrual blood loss. Nine studies recorded statistically significant average menstrual blood loss reductions with LNG-IUS (range 74%-97%). Another showed reduction in menstrual disturbance score. The LNG-IUS was more effective than tranexamic acid, but slightly less effective than endometrial resection at reducing menstrual blood loss. In one study, 64% of women cancelled surgery at six months, compared with 14% of control group women. In another, 82% were taken off surgical waiting lists at one year. No cost effectiveness studies were found.

DISCUSSION

Small studies of moderate quality indicate the LNG-IUS is an effective treatment for menorrhagia. Costs may be less than for tranexamic acid in primary and secondary care. Although its use may reduce surgical waiting lists, cost effectiveness assessment requires longer follow up.

CONCLUSION

Effectiveness and cost effectiveness relative to other treatments and the effect on surgical waiting lists can only be established in larger trials measuring patient-centred outcomes in women with menorrhagia.

Physical model for the spectroscopic analysis of cortical intrinsic optical signals

We used Monte Carlo simulations and the diffusion approximation to estimate correction terms for the analysis of reflectance spectra of cortical intrinsic optical signals. These corrections depend on scattering and absorption properties, i.e. they are dependent on assumptions on the tissue blood content and oxygen saturation. The analysis was applied to reflectance spectra acquired during whisker barrel stimulation in the rat where attenuation spectra were converted to changes in oxygenated and deoxygenated haemoglobin concentration. The description of the experimental data as judged by the residual and sensitivity to variations of wavelength was considerably improved when the correction terms were included. Inclusion of the correction does have a considerable impact on the time course of deoxyhaemoglobin concentration changes. In contrast to the calculation without correction terms, there is no indication for an early increase in deoxyhaemoglobin ('early dip'). This finding might further current interpretation of the coupling between neuronal activation and oxygen extraction and supply.

Mater, a maternal effect gene required for early embryonic development in mice

Maternal effect genes produce mRNA or proteins that accumulate in the egg during oogenesis. We show here that Mater, a mouse oocyte protein dependent on the maternal genome, is essential for embryonic development beyond the two-cell stage. Females lacking the maternal effect gene Mater are sterile. Null males are fertile.

Interactions of Escherichia coli RNA with bacteriophage MS2 coat protein: genomic SELEX

Genomic SELEX is a method for studying the network of nucleic acid-protein interactions within any organism. Here we report the discovery of several interesting and potentially biologically important interactions using genomic SELEX. We have found that bacteriophage MS2 coat protein binds several Escherichia coli mRNA fragments more tightly than it binds the natural, well-studied, phage mRNA site. MS2 coat protein binds mRNA fragments from rffG (involved in formation of lipopolysaccharide in the bacterial outer membrane), ebgR (lactose utilization repressor), as well as from several other genes. Genomic SELEX may yield experimentally induced artifacts, such as molecules in which the fixed sequences participate in binding. We describe several methods (annealing of oligonucleotides complementary to fixed sequences or switching fixed sequences) to eliminate some, or almost all, of these artifacts. Such methods may be useful tools for both randomized sequence SELEX and genomic SELEX.

Preference measurement using conjoint methods: an empirical investigation of reliability

The application of conjoint measurement to the field of health economics is relatively new, although there is growing interest and there have been a number of studies undertaken recently. Wider acceptance of the technique requires methodological issues concerning both reliability and validity to be addressed. This paper reports an empirical investigation of the test-retest reliability of the discrete choice conjoint measurement approach in health care. This investigation of conjoint reliability was framed using the clinical context of investigation and treatment of knee injuries. A high level of reliability at both the input data and results levels was demonstrated.

Aptamers as therapeutic and diagnostic agents

Aptamers are oligonucleotides derived from an in vitro evolution process called SELEX. Aptamers have been evolved to bind proteins which are associated with a number of disease states. Using this method, many powerful antagonists of such proteins have been found. In order for these antagonists to work in animal models of disease and in humans, it is necessary to modify the aptamers. First of all, sugar modifications of nucleoside triphosphates are necessary to render the resulting aptamers resistant to nucleases found in serum. Changing the 2'OH groups of ribose to 2'F or 2'NH2 groups yields aptamers which are long lived in blood. The relatively low molecular weight of aptamers (8000-12000) leads to rapid clearance from the blood. Aptamers can be kept in the circulation from hours to days by conjugating them to higher molecular weight vehicles. When modified, conjugated aptamers are injected into animals, they inhibit physiological functions known to be associated with their target proteins. A new approach to diagnostics is also described. Aptamer arrays on solid surfaces will become available rapidly because the SELEX protocol has been successfully automated. The use of photo-cross-linkable aptamers will allow the covalent attachment of aptamers to their cognate proteins, with very low backgrounds from other proteins in body fluids. Finally, protein staining with any reagent which distinguishes functional groups of amino acids from those of nucleic acids (and the solid support) will give a direct readout of proteins on the solid support.

The use of aptamers in large arrays for molecular diagnostics

BACKGROUND

Aptamers are single-stranded oligonucleotides derived from an in vitro evolution protocol called systematic evolution of ligands by exponential enrichment (SELEX). They bind tightly and specifically to target molecules; most aptamers to proteins bind with Kds (equilibrium dissociation constant) in the range of 1 pM to 1 nM.

METHODS AND RESULTS

The SELEX protocol has been automated; therefore, hundreds to thousands of aptamers can be made in an economically feasible fashion. Blood and urine can be analyzed on chips that capture and quantitate proteins. SELEX has been adapted to the use of 5-bromo (5-Br) and 5-iodo (5-I) deoxyuridine residues. These halogenated bases can be specifically cross-linked to proteins. Selection pressure during in vitro evolution can be applied for both binding specificity and specific photo-cross-linkability. These are sufficiently independent parameters to allow one reagent, a photo-cross-linkable aptamer, to substitute for two reagents, the capture antibody and the detection antibody, in a typical sandwich array. After a cycle of binding, washing, cross-linking, and detergent washing, proteins will be specifically and covalently linked to their cognate aptamers.

CONCLUSIONS

Because no other proteins are present on the chips, protein-specific stain will now show a meaningful array of pixels on the chip. Learning algorithms and retrospective studies should lead to a robust, simple, diagnostic chip.

Using the continuous quality improvement process to safely lower the cesarean section rate

BACKGROUND

In 1994 a five-year prospective observational study (including 38,541 singleton live-born deliveries) based on maternal and neonatal hospital administrative discharge data for DRGs 370-375 was launched at Cedars Sinai Medical Center (CSMC) in Los Angeles. In 1993 a cesarean section (C-section) reduction task force was first convened and several interventions were conducted and monitored during a two-year period. In 1995 CSMC joined the Institute for Healthcare Improvement's (IHI's) national collaborative on lowering C-section rates.

RESULTS

The first intervention involved physician education (grand rounds) and occurred during the preintervention baseline period. Providing physician-specific data had been implemented before participation in the IHI collaborative. Two other interventions were implemented before the collaborative versus 13 interventions after. The C-section rate decreased from 26.0% in the baseline period in 1993 to 20.5% in 1997, a 21.2% reduction. During the postintervention period, the C-section rate increased to 23.5%. There was no statistically or clinically significant increase in clavicular fractures, brachial plexus injuries, or cerebral hemorrhage in the four study years, compared to the baseline period.

DISCUSSION

It is possible to safely reduce C-section delivery rates. Activities are now under way to involve additional private physician leaders in the continuous quality improvement effort. Although the small increase in the C-section rate during the postintervention period may represent statistical variation, and in itself may not be clinically significant, it supports the thesis that ongoing, continuous organizational support is required to achieve and maintain gains.

Incorporation of mouse zona pellucida proteins into the envelope of Xenopus laevis oocytes

All vertebrate eggs have extracellular matrices, referred to as the zona pellucida in Mus musculus and the vitelline envelope in Xenopus laevis. The mouse zona, composed of three sulfated glycoproteins (ZP1, ZP2, ZP3), is critical for fertilization and early development, and mice lacking a zona pellucida produce no live offspring. The primary structures of mouse ZP1 (623 amino acids), ZP2 (713 amino acids) and ZP3 (424 amino acids) have been deduced from full-length cDNAs, but posttranslational modifications result in mature zona proteins with molecular masses of 200-180 kDa, 140-120 kDa, and 83 kDa, respectively. The vitelline envelope forms a similar structure around Xenopus eggs and contains three glycoproteins that are structurally related (39-48% amino acid similarity) to the three mouse zona proteins. To investigate whether the structural semblances are sufficient to allow incorporation of the mouse zona proteins into the Xenopus vitelline envelope, capped synthetic mRNAs encoding ZP1, ZP2, and ZP3 proteins were injected into the cytoplasm of stage VI Xenopus oocytes. After 20 h of incubation the oocytes were harvested, and posttranslationally modified zona proteins were detected with monoclonal antibodies specific to mouse ZP1, ZP2, and ZP3. The oocytes were imaged with confocal microscopy to detect individual zona proteins in the extracellular matrix of the oocytes, and this localization was confirmed biochemically. Thus the mouse zona proteins appear to have been sufficiently conserved through 350 million years of evolution to be incorporated into the extracellular envelope surrounding Xenopus eggs.

Perivascular nerves contribute to cortical spreading depression-associated hyperemia in rats

We investigated the contribution of perivascular nerves and neurotransmitters to cortical spreading depression (CSD)-associated hyperperfusion in the rat. Chronic transection of the nasociliary nerve (NCN, 2 wk before) decreased ipsilateral CSD-associated hyperperfusion by 23 +/- 13% (mean +/- SD; n = 5, P < 0.05), whereas acute transection of the NCN or sham surgery had no effect (n = 8). When the NCN and parasympathetic nerve fibers (PSN) were both chronically transected, CSD hyperperfusion was attenuated by 55 +/- 19% (n = 5, P < 0.05). Cerebrovascular reactivity to hypercapnia was not significantly affected. Brain topical superfusion of the muscarinic receptor antagonist atropine (10(-4) M) caused a reduction of CSD hyperperfusion by 41 +/- 13% (n = 5, P < 0.05). The competitive blockade of calcitonin gene-related peptide (CGRP) receptors by CGRP-(8-37) (5 x 10(-7) M) afforded a decrease by 49 +/- 19% (n = 5, P < 0.05), without affecting CO2 reactivity (n = 4). The combined application of both CGRP-(8-37) and atropine further attenuated CSD hyperperfusion (by 69 +/- 17%, n = 5, P < 0.05). After chronic NCN and PSN transection brain topical superfusion of CGRP-(8-37) (5 x 10(-7) M) reduced CSD hyperperfusion slightly by 9.5 +/- 5% (n = 3). Atropine (10(-4) M) afforded a decrease by 17 +/- 6% (n = 3). These reductions were not statistically significant. We conclude that CSD-associated hyperperfusion is mediated in part by a depolarization of trigeminal sensory and parasympathetic nerve fibers, resulting in a release of vasoactive trigeminal and parasympathetic neurotransmitters.

The mathematics of SELEX against complex targets

We have developed a computer model for the simulation of simultaneous SELEX against multiple targets. The model assumes equilibrium behavior for the formation of binary ligand:target complexes, and that there is no ligand:ligand or target:target interaction. Target concentrations, ligand concentrations, and affinity distributions of the initial ligand pool for each individual target may be set by the user. We have used this program to gain an understanding of how the presence of multiple targets affects the selection process. In most cases, we find that SELEX is capable of generating different ligands for the different targets in a heterogeneous mixture, regardless of large variations in target concentrations and ligand:target affinities. A low relative partitioning efficiency (the efficiency with which ligands complexed with a target are separated from free ligands) for a target in a mixture gives a greatly reduced rate of selection of high-affinity ligands to that target. The ratio of each high-affinity ligand to its individual target within a pool of ligands selected for binding against a mixture of targets is approximately proportional to the concentration of the target multiplied by the ligand:target partitioning efficiency.

High affinity ligands from in vitro selection: complex targets

Human red blood cell membranes were used as a model system to determine if the systematic evolution of ligands by exponential enrichment (SELEX) methodology, an in vitro protocol for isolating high-affinity oligonucleotides that bind specifically to virtually any single protein, could be used with a complex mixture of potential targets. Ligands to multiple targets were generated simultaneously during the selection process, and the binding affinities of these ligands for their targets are comparable to those found in similar experiments against pure targets. A secondary selection scheme, deconvolution-SELEX, facilitates rapid isolation of the ligands to targets of special interest within the mixture. SELEX provides high-affinity compounds for multiple targets in a mixture and might allow a means for dissecting complex biological systems.

Cortical spreading depression-associated hyperemia in rats: involvement of serotonin

We investigated whether the vasoactive neurotransmitter serotonin (5-HT) is involved in cortical spreading depression (CSD)-associated hyperemia in the rat. We focused on the 5-HT2 receptor, which is engaged in 5-HT induced small arteriolar relaxation in cats, as well as on the 5-HT1D/1B receptor, the binding site of the potent antimigraine drug sumatriptan. In male barbiturate anaesthetized Wistar rats (n=25) CSDs were elicited by brain topical application of 1 M KCl, and the DC-potential and regional cerebral blood flow (rCBF, by Laser Doppler flowmetry) were measured over the same hemisphere through dura and thinned bone, respectively. Intravenous application of 8 mg/kg of the 5-HT2A/2C receptor antagonist ritanserin (group I; n=8) significantly reduced the hyperperfusion amplitude during CSD by approximately 44% (p<0.05, from 342+/-124 to 194+/-97%, baseline before CSD=100%), and prolonged its duration by approx. 30%. Vehicle alone (group II; n=4) did not affect CSD hyperperfusion. The highly selective 5-HT1D/1B receptor agonist 311C90 was given in two doses: 100 micrograms/kg i.v. (n=5) had no effect on CSD hyperperfusion, while 800 micrograms/kg (n=5) increased hyperperfusion significantly (p<0.05, from 224+/-86 to 310+/-148%). We conclude that serotonin is, probably via 5-HT2 receptors, involved in the modulation of the regional cerebral blood flow increase during CSD. Novel highly selective receptor antagonists may help to discriminate the differential contribution of various 5-HT receptor subspecies.

SELEX and the evolution of genomes

The interrupted genome structures of complex multicellular organisms have most likely changed the evolution of the regulation of metabolism and development. Wasted intron sequences make regulation of gene expression in (for example) mammals appear to be unnecessarily complicated. The recent discoveries that globular RNA molecules are very much like the antigen-combining sites of antibodies suggest that intronic RNA may be used to help solve the problems raised by this complexity.

RNA aptamers to the peptidyl transferase inhibitor chloramphenicol

BACKGROUND

The problem of how macromolecules adopt specific shapes to recognize small molecules in their environment is readily addressed through in vitro selections (the SELEX protocol). RNA-antibiotic interactions are particularly attractive systems for study because they provide an opportunity to expand our understanding of molecular recognition by RNA and to facilitate ribosomal modeling. Specifically, the antibiotic chloramphenicol (Cam) naturally binds bacterial ribosomes in the 'peptidyl transferase loop' of 23S ribosomal RNA to inhibit peptide bond formation.

RESULTS

We identified Cam-binding RNA molecules ('aptamers') from two independent initial random RNA populations. Boundary determinations, ribonuclease S1 sensitivity analyses and the activity of truncated minimal RNAs identified a structural motif that is shared by sequences from both selections. The pseudosymmetric motif consists of a highly conserved central helix of five to six base pairs flanked by A-rich bulges and additional helices. Addition of Cam prior to ribonuclease S1 protected nucleotides in the conserved cores from cleavage. Reselection from a pool of mutated variants of the minimal aptamer further refined the sequence requirements for binding. Finally, we used proton nuclear magnetic resonance (NMR) to establish a 1:1 RNA: Cam stoichiometry of the complex. Both the protection and NMR data both show that Cam stabilizes the active fold of this aptamer.

CONCLUSIONS

There are many different RNA sequences that can bind Cam. The Cam aptamers that we examined have a well-defined secondary structure with a binding pocket that appears to be stabilized by Cam. This RNA motif superficially resembles the Cam-binding site in 23S rRNA, although further work is needed to establish the significance of these similarities.