Attempts to develop efficient classification approaches to the problem of heterogeneity in single-particle reconstruction of macromolecules require phantom data with realistic noise models. We have estimated the signal-to-noise ratios and spectral signal-to-noise ratios for three steps in the electron microscopic image formation from data obtained experimentally. An important result is that structural noise, i.e., the irreproducible component of the object prior to image formation, is substantial, and of the same order of magnitude as the reproducible signal. Based on this result, the noise modeling for testing new classification techniques can be improved.

10aCryoelectron Microscopy10aImage Processing, Computer-Assisted1 aBaxter, Bill1 aGrassucci, Robert, A1 aGao, Haixiao1 aFrank, Joachim uhttp://www.ncbi.nlm.nih.gov/pubmed/1926933201752nas a2200265 4500008004100000022001400041245010100055210006900156260001200225300001000237490000800247520093400255653002801189653002101217653002201238653004001260653001401300100002001314700002501334700002201359700001701381700002101398700001901419856004801438 2008 eng d a1095-865700aExploration of parameters in cryo-EM leading to an improved density map of the E. coli ribosome.0 aExploration of parameters in cryoEM leading to an improved densi c10/2008 a24-320 v1643 aA number of image processing parameters in the 3D reconstruction of a ribosome complex from a cryo-EM data set were varied to test their effects on the final resolution. The parameters examined were pixel size, window size, and mode of Fourier amplitude enhancement at high spatial frequencies. In addition, the strategy of switching from large to small pixel size during angular refinement was explored. The relationship between resolution (in Fourier space) and the number of particles was observed to follow a lin-log dependence, a relationship that appears to hold for other data, as well. By optimizing the above parameters, and using a lin-log extrapolation to the full data set in the estimation of resolution from half-sets, we obtained a 3D map from 131,599 ribosome particles at 6.7A resolution (FSC=0.5).

10aCryoelectron Microscopy10aEscherichia coli10aImage Enhancement10aImage Processing, Computer-Assisted10aRibosomes1 aLeBarron, Jamie1 aGrassucci, Robert, A1 aShaikh, Tanvir, R1 aBaxter, Bill1 aSengupta, Jayati1 aFrank, Joachim uhttp://www.ncbi.nlm.nih.gov/pubmed/18606549