Ribosomal frameshifting occurs when a ribosome slips a few nucleotides on an mRNA and generates a new sequence of amino acids. Programmed −1 ribosomal frameshifting (−1PRF) is used in various systems to express two or more proteins from a single mRNA at precisely regulated levels. We used single-molecule fluorescence resonance energy transfer (smFRET) to study the dynamics of −1PRF in the Escherichia coli dnaX gene. The frameshifting mRNA (FSmRNA) contained the frameshifting signals: a ShineDalgarno sequence, a slippery sequence, and a downstream stem loop. The dynamics of ribosomal complexes translating through the slippery sequence were characterized using smFRET between the Cy3-labeled L1 stalk of the large ribosomal subunit and a Cy5-labeled tRNA Lys in the ribosomal peptidyl-tRNA-binding (P) site. We observed significantly slower elongation factor G (EF-G)-catalyzed translocation through the slippery sequence of FSmRNA in comparison with an mRNA lacking the stem loop, ΔSL. Furthermore, the P-site tRNA/L1 stalk of FSmRNA-programmed pretranslocation (PRE) ribosomal complexes exhibited multiple fluctuations between the classical/open and hybrid/closed states, respectively, in the presence of EF-G before translocation, in contrast with ΔSL-programmed PRE complexes, which sampled the hybrid/closed state approximately once before undergoing translocation. Quantitative analysis showed that the stimulatory stem loop destabilizes the hybrid state and elevates the energy barriers corresponding to subsequent substeps of translocation. The shift of the FSmRNA-programmed PRE complex equilibrium toward the classical/open state and toward states that favor EF-G dissociation apparently allows the PRE complex to explore alternative translocation pathways such as −1PRF.programmed ribosomal frameshifting | ribosomal dynamics | single-molecule FRET | mRNA secondary structure T he ribosome is the molecular machine that synthesizes proteins by translating messenger RNAs (mRNAs); each sequence of 3 nt, 1 codon, characterizes 1 aa (1-3). Failure to maintain frame during translation occurs with a low error of 10 −5 (4); however, frameshifting with high efficiency (>10 −2 ) is often programmed into many mRNAs to express two or more proteins from a single mRNA (5, 6). Many RNA viruses, including HIV-1, use programmed frameshifting to produce their vital proteins at a precise ratio (7,8). The common −1 programmed ribosomal frameshifting (−1PRF) signals are a heptanucleotide slippery sequence (X XXY YYZ, underlining denotes the zero-frame) and a downstream stimulatory secondary structure such as a stem loop or a pseudoknot. Frameshifting that takes place on the slippery sequence results in minimal base pair mismatches. Prokaryotic systems have an additional stimulatory signal, an upstream, internal Shine-Dalgarno (SD) sequence (9). The dnaX gene of Escherichia coli has the three −1PRF signals; an SD sequence, an A AAA AAG slippery sequence, and a downstream stem loop (9-12). Highly efficient (50-80%) −1PRF during translation of the mRN...

Purpose:To analyze T2 maps of pelvic and thigh muscles in Duchenne muscular dystrophy (DMD), to identify the most severely affected muscle, and to correlate the T2 of muscle with the grade of fatty infi ltration at nonquantitative magnetic resonance (MR) imaging and results of clinical assessment . Materials and Methods:This prospective study was HIPAA compliant and was approved by the institutional review board; written consent was obtained from all participants' parents or guardians. Thirty-four boys with DMD (mean age, 8.4 years) were evaluated clinically (age, clinical function score, timed Gower score, time to run 30 feet, and serum creatine kinase [CK] level) and with nonquantitative MR imaging and axial T2 mapping from the iliac crest to the mid thigh. The T2 maps and mean T2 of 18 muscles in the pelvis and thighs were analyzed to identify the most severely involved muscle. The amount of fatty infi ltration was assigned a grade of zero to four for all pelvic and thigh muscles by using T1-weighted nonquantitative MR images. The Spearman correlation coeffi cients model was used to correlate the mean T2, nonquantitative MR imaging score and clinical assessments. Results:The gluteus maximus muscle had the highest T2. The mean T2 for this muscle showed a signifi cant correlation with the nonquantitative MR imaging score for fatty infi ltration ( P , .001) and with all clinical assessments except CK level. Conclusion:Gluteus maximus muscles are most severely affected in patients with DMD. The T2 of the gluteus maximus muscle can be used as a quantitative and objective measure of disease severity.q RSNA, 2010

Smart agents. A contrast agent was designed by combining target specific nucleic‐acid aptamers against adenosine with superparamagnetic iron oxide nanoparticles. Target‐induced disassembly of clustered nanoparticles in the presence of adenosine led to an increase in T2, which was seen as an increase in the brightness of the magnetic resonance image (see figure).

PURPOSEThis study investigated the effect of amount of thickness reduction on color and translucency of dental monolithic zirconia ceramics.MATERIALS AND METHODSOne-hundred sixty-five monolithic zirconia specimens (16.3 mm × 16.3 mm × 2.0 mm) were divided into 5 groups (Group I to V) according to the number of A2-coloring liquid applications. Each group was then divided into 11 subgroups by reducing the thickness up to 1.0 mm in 0.1-mm increments (Subgroup 0 to 10, n=3). Colors and spectral distributions were measured according to CIELAB on a reflection spectrophotometer. All measurements were performed on five different areas of each specimen. Color difference (ΔE*ab) and translucency parameter (TP) were calculated. Data were analyzed using one-way ANOVA and multiple comparison Scheffé test (α=.05).RESULTSThere were significant differences in CIE L* between Subgroup 0 and other subgroups in all groups. CIE a* increased (0.523.7) were obtained between Subgroup 0 and other subgroups. TP values generally increased as the thickness reduction increased in all groups (R2>0.89, P<.001).CONCLUSIONIncreasing thickness reduction reduces lightness and increases a reddish, bluish appearance, and translucency of monolithic zirconia ceramics.