EM Sample
Sample Vitrification Details No vitrification. Samples were viewed at room temperature.
Sample Aggregation State TISSUE
Name of Sample Insect flight muscle
Sample Details Dorsal longitudinal flight muscles of the large waterbug, Lethocerus maximus were glycerinated in the dissected thorax and stored at -20 degrees C. Fixation involved sequential tannic acid-glutaraldehyde (0.2% and 2%), cold 1% OsO4 at pH 6.0, 1% uranyl acetate block staining and Araldite 506 emgedding. Thin sections were stained with a sequence of permanganate and lead. Section were ~25 nm thick.
EM Data Acquisition
Date of Experiment --
Num of Micrographs-Images Used 36
Temperature (Kelvin) --
Microscope Model --
Detector Type Kodak S0163 Film
Minimum Defocus (nm) --
Maximum Defocus (nm) --
Minimum Tilt Angle (degrees) --
Maximum Tilt Angle (degrees) --
Nominal CS --
Imaging Mode --
Electron Dose (electrons nm**-2) --
Illumination Mode --
Nominal Magnification --
Calibrated Magnification --
Source --
Acceleration Voltage (kV) --
Imaging Details --
3D Reconstruction
Software Package(s)
Reconstruction Method Dual axis tilt series electron tomography
EM Image Reconstruction Statistics
Nominal Pixel Size 15.5
Effective Resolution 70.0
CTF Correction Method none
EM Reconstruction Magnification Callibration Indicated instrument magnification
Other Details 3-D motifs were identified in the tomogram by first producing a cross correlation map from which peak coordinates were determined from their center of gravity. We define a 3-D motif as one, entire 38.7 nm crossbridge repeat along actin. These motifs usually contain at least four myosin heads in two paired crossbridges (single chevrons) and sometimes contain as many as six myosin heads in four paired crossbridges (double chevrons). The reference for the analysis was selected to be centered between successive troponin densities which could be identified from the in-plane projection. The individual crossbridge motifs were then subjected to multivariate statistical analysis to identify clusters of motifs showing similar crossbridge structure. These clusters formed the class averages. The choice of structure to be classified was decided by the resolution and the later process of model building. Averaging was done according to the heirarchical ascendent method. The resolution in each of the class averages was 7 nm by the spectral signal to noise ratio.
EM Map-Model Fitting and Refinement
Refinement Space Refinement Protocol Refinement Target Overall B Value Fitting Procedure Fitting Software
REAL rigid body Best correlation coefficient and fewest poor contacts -- Initial models were fit by hand using "O". The fit was then refined using real space refinement. RSref