With the increase in the number of large, 3D, high-resolution nucleic acid structures, particularly of the 30S and 50S ribosomal subunits and the intact bacterial ribosome, advancements in the visualization of nucleic acid structural features are essential. Large molecular structures are complicated and detailed, and one goal of visualization software is to allow the user to simplify the display of some features and accent others. We describe an extension to the UCSF Chimera molecular visualization system for the purpose of displaying and highlighting nucleic acid characteristics, including a new representation of sugar pucker, several options for abstraction of base geometries that emphasize stacking and base pairing, and an adaptation of the ribbon backbone to accommodate the nucleic acid backbone. Molecules are displayed and manipulated interactively, allowing the user to change the representations as desired for small molecules, proteins and nucleic acids. This software is available as part of the UCSF Chimera molecular visualization system and thus is integrated with a suite of existing tools for molecular graphics.

The design, implementation, and capabilities of an extensible visualization system, UCSF Chimera, are discussed. Chimera is segmented into a core that provides basic services and visualization, and extensions that provide most higher level functionality. This architecture ensures that the extension mechanism satisfies the demands of outside developers who wish to incorporate new features. Two unusual extensions are presented: Multiscale, which adds the ability to visualize large-scale molecular assemblies such as viral coats, and Collaboratory, which allows researchers to share a Chimera session interactively despite being at separate locales. Other extensions include Multalign Viewer, for showing multiple sequence alignments and associated structures; ViewDock, for screening docked ligand orientations; Movie, for replaying molecular dynamics trajectories; and Volume Viewer, for display and analysis of volumetric data. A discussion of the usage of Chimera in real-world situations is given, along with anticipated future directions. Chimera includes full user documentation, is free to academic and nonprofit users, and is available for Microsoft Windows, Linux, Apple Mac OS X, SGI IRIX, and HP Tru64 Unix from http://www.cgl.ucsf.edu/chimera/.

We describe the Object Technology Framework (OTF) software system developed at the University of California, San Francisco Computer Graphics Laboratory for creating C+2 classes that facilitate rapid biomolecular application development and the application of the OTF to collagen modeling. C+2 class libraries for accessing and manipulating data from standard scientific data sources can be generated using the program genlib and its class library toolkit Molecule, thereby facilitating development of new applications. Use of the OTF for generating ideal collagen structural models (gencollagen) is described. The source code for the OTF is freely available at http:/(/)www.cgl.ucsf.edu/off/ to interested application developers.

We have implemented extensions to the Brookhaven Protein Data Bank (PDB) file format for incorporating scene information such as viewing parameters, additional molecular information (e.g., van der Waals radii and atom colors), and user-defined graphics. These extensions were made in conformance with the PDB standard and provide sufficient information to render the scene in various styles such as space-filling images and ribbon diagrams. For the past 5 years these extensions have been used in the MidasPlus molecular modeling system and have proved both powerful and sufficient for generating complex molecular images. We propose that the extensions to the PDB presented here be adopted by the molecular modeling community for incorporation into visualization programs.

The amazing revolution in computer hardware performance and cost reduction has yet to be carried over to computer software. In fact, application software today is often more expensive and less reliable than the hardware. New enhancements in software development techniques, such as object oriented programming and interactive graphics based user interface design, finally may be having a significant impact on the time-to-market and reliability of these application programs. We discuss our experiences using one such set of software development tools available on the NeXT workstation and describe the effort required to port our MidasPlus molecular modeling package to the NeXT workstation.

We describe a method for generating a molecular surface using a parametric patch representation. Unlike previous methods, this algorithm generates a parametric patch surface which is smooth and G continuous and manipulable in real-time. Crucial to our approach is the creation of a net of approximately equilateral triangles from which we generate the control points used as the basis for describing the surface. We present in detail the method used for generating the triangular net and accompanying control points, along with examples of the resulting surfaces.

The infrared dichroic ratios of the amide bands from oriented β-barrels yield an experimental value for the mean orientation, β, of the β-strands, relative to the barrel axis. For a barrel of n strands, this then gives the shear number, S, that characterizes the stagger of the β-sheet. Combining values of β and n specifies the barrel geometry by using the optimized model of Murzin, Lesk & Chothia for regular barrels. Application to published infrared data on the Escherichia coli outer membrane protein, OmpA yields S=9−10 (n=8), a barrel radius of 0.81(±0.01) nm, and an internal free volume of 0.031 nm3 per residue, where the average twist of the β-sheets is θ≈28 °, and their coiling angle is ϵ≈1 °. Hydrophobic matching of the 2.6 nm transmembrane stretch partly determines the shear number of the OmpA β-barrel.