Hi Abhijit, If I understand correctly, there were two questions here:

One more question is it possible to take a protein sequence of a gene, part of which is cloned, crystallized and 3d structure is available, and superimposes the protein sequence with the reported crystal structure? Or how can you model a protein sequence to generate a putative structure, for the part that hasn’t been crystallized so far,

In Chimera, (1) can you associate a structure with a sequence that is read in from a separate file? short answer: yes, if that sequence is in an alignment (2) can you do comparative modeling (create a 3D model of an unknown structure starting from a known structure that is thought to be similar)? short answer: no, except simplistic replacement of a few side chains with the command "swapaa" I'll start with #2: Chimera does not do comparative modeling or threading different sequences on a known structure. Besides the approaches mentioned by Eric (getting a model from MODBASE or using the MODELLER program to make the model yourself), listed below are several web servers that might be useful. I believe the first two replace side chains while the others perform more complete modeling (can handle insertions/deletions and adjust the backbone). It's been a while since I used any of these, however, so you should read any author-provided information. - SCWRL server http://www1.jcsg.org/scripts/prod/scwrl/serve.cgi - Maxsprout server http://www.ebi.ac.uk/maxsprout/ - ModWeb server (requires registration) http://alto.compbio.ucsf.edu/modweb-cgi/main.cgi - RAPPER server (registration encouraged) http://mordred.bioc.cam.ac.uk/~rapper/ - PSIPRED server http://bioinf.cs.ucl.ac.uk/psipred/ - Swiss-Model server http://swissmodel.expasy.org//SWISS-MODEL.html Now question #1. You already saw the Sequence tool, which shows the exact sequence of any peptide or nucleotide chains in structures open in Chimera. However, you might want to read in a sequence from a separate file and associate it with the structure to allow the same kinds of crosstalk (a selection on the sequence selects the structure and vice versa). You can do that, if you have an alignment of that sequence with one or more additional sequences. These other sequences don't need to have any structures, and your sequence of interest does not have to match the structure exactly to associate with it (often there are point mutations, or the sequence is for a close homolog of the structure, or the structure is missing a few residues here and there, or is only one domain from the whole sequence). Here's a list of the sequence alignment formats that can be read (you can just use File... Open in the Chimera menu): http://www.cgl.ucsf.edu/chimera/docs/UsersGuide/filetypes.html#alignment and the "Sequence-Structure Association" section in this page may be useful: http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/ multalignviewer/framemav.html I hope this helps, 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