One option is to change the chain IDs and residue numbers manually using a text editor like nedit. Sent from Jack's iPad On Oct 23, 2014, at 6:03 AM, luzuok <[log in to unmask]<mailto:[log in to unmask]>> wrote: Dear all, Sorry to ask a simple question. There are many SO4 in my PDB file, one belongs to a different chain. I want to merge them into one chain, can anyone tell me how to do this? Best regards! Lu Zuokun -- 卢作焜 南开大学新生物站A202