Identification of a radical SAM enzyme involved in the synthesis of archaeosine.

Archaeosine (G+), 7-formamidino-7-deazaguanosine, is an archaea-specific modified nucleoside found at the 15th position of tRNAs. In Euryarchaeota, 7-cyano-7-deazaguanine (preQ0)-containing tRNA (q0N-tRNA), synthesized by archaeal tRNA-guanine transglycosylase (ArcTGT), has been believed to be converted to G+-containing tRNA (G+-tRNA) by the paralog of ArcTGT, ArcS. However, we found that several euryarchaeal ArcSs have lysine transfer activity to q0N-tRNA to form q0kN-tRNA, which has a preQ0 lysine adduct as a base. Through comparative genomics and biochemical experiments, we found that ArcS forms a robust complex with a radical S-adenosylmethionine (SAM) enzyme named RaSEA. The ArcS-RaSEA complex anaerobically converted q0N-tRNA to G+-tRNA in the presence of SAM and lysine via q0kN-tRNA. We propose that ArcS and RaSEA should be considered an archaeosine synthase α-subunit (lysine transferase) and ß-subunit (q0kN-tRNA lyase), respectively.

Mandibular Jaw Movement and Masticatory Muscle Activity during Dynamic Trunk Exercise.

The examination of jaw movement during exercise is essential for an improved understanding of jaw function. Currently, there is no unified view of the mechanism by which the mandible is fixed during physical exercise. We hypothesized that during strong skeletal muscle force exertion in dynamic exercises, the mandible is displaced to a position other than the maximal intercuspal position and that mouth-opening and mouth-closing muscles simultaneously contract to fix the displaced mandible. Therefore, we simultaneously recorded mandibular jaw movements and masticatory muscle activities during dynamic trunk muscle force exertion (deadlift exercise) in 24 healthy adult males (age, 27.3 ± 2.58 years). The deadlift was divided into three steps: Ready (reference), Pull, and Down. During Pull, the mandibular incisal point moved significantly posteriorly (-0.24 mm, p = 0.023) and inferiorly (-0.55 mm, p = 0.019) from the maximal intercuspal position. Additionally, temporal, masseter, and digastric muscles were activated simultaneously and significantly during Pull (18.63 ± 17.13%, 21.21 ± 18.73%, 21.82 ± 19.97% of the maximum voluntary contraction, respectively), with maintained activities during Down (p < 0.001). Thus, during dynamic trunk muscle force exertion, the mandibular incisal point moved to a posteroinferior position without tooth-touch (an open-mouth position). Simultaneously, the activities of the mouth-opening digastric muscles and the mouth-closing temporal and masseter muscles led to mandibular fixation, which is a type of mandible fixing called bracing.

Steepening of corneal curvature with contraction of the ciliary muscle.

PURPOSE: To measure the changes of corneal curvature during contraction of the ciliary muscle. SETTING: Department of Ophthalmology, St. Luke's International Hospital, Tokyo, Japan. METHODS: Twenty-eight eyes of 14 healthy volunteers under 40 years old were enrolled in this prospective randomized controlled study and divided into pilocarpine and control groups. Intraocular pressure (IOP), pupil diameter, and corneal topography were measured before and 40 minutes after instillation of topical pilocarpine 4% or balanced salt solution. Corneal topography was analyzed for the mean ring-power of Placido rings 1 through 25, average corneal power (ACP), and for spherical equivalent, regular astigmatism, asymmetry, and high-order irregularity by Fourier analysis. RESULTS: Pilocarpine had no effect on IOP, but it did cause a significant decrease in mean pupil diameter. Simultaneously, pilocarpine increased the mean ring powers for Placido rings 1 through 4 and the ACP (+0.13 diopters (D) +/- 0.17 [SD]; P=.017). By Fourier analysis, the mean spherical component for the central 3.0 mm of the cornea increased in the pilocarpine group (+0.08 +/- 0.15 D; P=.020). There were no changes in components of regular astigmatism, asymmetry, and high-order irregularity. CONCLUSIONS: The central cornea steepened in curvature and increased in power owing to contraction of the ciliary muscle. The results suggest that changes in corneal curvature increase refractive power during accommodation.

Changes in corneal curvature in accommodation.

PURPOSE: To determine the changes in corneal curvature in accommodation. SETTING: Department of Ophthalmology, St. Luke's International Hospital, Tokyo, Japan. METHODS: Twenty-eight eyes of 14 healthy volunteers with a mean age of 38.9 years (range 28 to 65 years) were enrolled in this prospective study. Corneal topographies were taken before and during accommodation. Subjects achieved maximal accommodation by gazing at a target letter "A" in front of the eye. Keratometric values (K-values) obtained by topographies before and during accommodation were compared. RESULTS: Steepened corneal curvatures during accommodation were observed with the difference-plot view. Maximum K-values for the central 3.0 mm, 5.0 mm, and 7.0 mm corneal diameters significantly increased by a mean of 0.62 diopters (D) +/- 0.83 (SD) (P =.0005, paired t test), 0.60 +/- 0.90 D (P =.0015), and 0.72 +/- 0.65 D (P<.0001), respectively. Respective minimum K-values significantly increased by a mean of 0.62 +/- 0.83 D (P=.0005), 0.67 +/- 0.68 D (P<.0001), and 0.64 +/- 0.62 D (P<.0001). No statistically significant relationship was found between age and change in K-values. CONCLUSION: The results suggest that changes in corneal curvature in accommodation participate in the mechanism of accommodation.

Algicidal activity and gliding motility of Saprospira sp. SS98-5.

A marine bacterium, Saprospira sp. SS98-5, which was isolated from Kagoshima Bay, Japan, was able to kill and lyse the cells of the diatom Chaetoceros ceratosporum. The multicellular filamentous cells of this bacterium captured the diatom cells, formed cell aggregates, and lysed them in an enriched sea water (ESS) liquid medium. Strain SS98-5 also formed plaques on double layer agar plates incorporating diatom cells. The diatom cell walls were partially degraded at the contact sites with the bacteria, the bacteria invaded from there into the diatom cells, and then the diatom cells were completely lysed. The strain possessed gliding motility and grew as spreading colonies on ESS agar plates containing lower concentrations of polypeptone (below 0.1%) while forming nonspreading colonies on ESS agar plates containing 0.5% polypeptone. Electron micrographs of ultrathin sections demonstrated that microtubule-like structures were observable only in gliding motile cells. Both the gliding motility and the microtubule-like structures were diminished by the addition of podophyllotoxin, an inhibitor of microtubule assembly, suggesting that the microtubule-like structures observed in these bacterial cells are related to their gliding motility.