I have a PDB of protein - DNA complex but this PDB only has single stranded DNA and I want double stranded DNA. So, is it possible to generate double stranded DNA from single stranded DNA of a particular protein - DNA complex?
1) You can download the biological unit of the PDB from ftp://ftp.wwpdb.org/pub/pdb/data/biounit/coordinates/all/.
2) You can calculate the coordinates of the missing subunits from the BIOMT transformation matrices contained in the pdb file.
If you are planning on doing the 2nd option, I highly recommend the usage of the following server: http://watcut.uwaterloo.ca/cgi-bin/makemultimer/. I guess the script MakeMultimer.py can also be downloaded from the internet.