Hi Francesco, It might work to put the matrices from the template into the homology model PDB file. Just be aware that the resulting multimer would be approximate and might have atoms from different monomers clashing with each other. You can see how it turns out and use your judgement as to whether it is good enough, and of course say what you had done if you were describing the work in a paper. After putting the matrix information in the homology model file, you would then proceed as with the original template structure to build the multimer in Chimera. Depending on the structure, you might want not only BIOMT, but also MTRIX, SMTRY and CRYST1 lines. Also be aware that it is fairly common for such information in a PDB file to be wrong, or only set to "identity" (regenerates the same coordinates already present in the file). However, if generating a multimer already worked for the template structure, that is not a concern. As mentioned in this previous mail to you, multimers can be built from symmetry information using "Unit Cell" or "Multiscale Models": http://www.cgl.ucsf.edu/pipermail/chimera-users/2007-October/001897.html Yet another way is with the command "sym": http://www.cgl.ucsf.edu/chimera/docs/UsersGuide/midas/sym.html "Unit Cell" does not use BIOMT, but the other two methods can handle that type of information. Other than using Chimera, you might want to see whether Modeller can just build the multimer in the first place, given a multimer template. Best, Elaine ----- Elaine C. Meng, Ph.D. meng@cgl.ucsf.edu UCSF Computer Graphics Lab and Babbitt Lab Department of Pharmaceutical Chemistry University of California, San Francisco http://www.cgl.ucsf.edu/home/meng/index.html On Jul 25, 2008, at 10:32 AM, Francesco Pietra wrote:

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From a homotrimer pdb template I have created (with Modeler) a homology model, with very good score, using a single subunit. Is it possible with Chimera to create the homology homotrimer, as this is what I need? To this concern, the original pdb for the template includes the BIOMT transformation matrix for both crystallographic and non-crystallographic operation. That is, the pdb includes as many identical chains to open directly the homotrimer for the crystallographic pose. Is that BIOMT matrix usable by Chimera for the homology model? Or the way ti take is another one?

I used much technical language, well above - however - my expertise in these affairs. That in view of any help, for which I'll be most grateful.

Thanks francesco pietra