HI there,

I am working my way through the tutorials, playing with the Python scripts to get a better understanding of how things work. I have successfully done a multiple structural alignment using a modified version of the salign.py script in the advanced tutorial aligning multiple sequences for a protein from several different species using the pdb files as input. The protein is a homopentamer, and using the example script, I aligned the "A" chains and everything worked fine. Since I really want to work on modeling a homopentamer, I then tried to do the alignment on the pentamers. I receive the following error: ************************************************************************* linux:/home/mike/Modeller_files/Modelling_projects/Test_run/Mult_align # mod8v2 salignPentamer.py Traceback (most recent call last): File "salignPentamer.py", line 11, in ? mdl = model(env, file=code, model_segment=('FIRST:@, LAST:')) File "/usr/bin/modeller8v2/modlib/modeller/model.py", line 23, in __init__ self.read(io, aln, libs, **vars) File "/usr/bin/modeller8v2/modlib/modeller/model.py", line 40, in read io=io.modpt, libs=libs.modpt, **vars) File "/usr/bin/modeller8v2/modlib/modeller/util/top.py", line 189, in read_model return _modeller.read_model(mdl, aln, io, libs, *args) ValueError: Expected a sequence for model_segment *************************************************************************

I assume that the problem is in reading the pdb files and getting the information.The pdb files do contain the chain ID's (A-E). Here is the Python script I used, which is essentially a slightly modified version of the example script:

*********************************************************************

from modeller import *

log.verbose() env = environ() env.io.atom_files_directory = './:../atom_files/'

aln = alignment(env) for (code, chain) in (('1i9b', 'A'), ('2br7', 'A'), ('2bj0', 'A')): mdl = model(env, file=code, model_segment=('FIRST:@, LAST:')) aln.append_model(mdl, atom_files=code, align_codes=code+chain)

for (weights, write_fit, whole) in (((1., 0., 0., 0., 1., 0.), False, True), ((1., 0.5, 1., 1., 1., 0.), False, True), ((1., 1., 1., 1., 1., 0.), True, False)): aln.salign(rms_cutoffs=(3.5, 6., 60, 60, 15, 60, 60, 60, 60, 60, 60), normalize_pp_scores=False, rr_file='$(LIB)/as1.sim.mat', overhang=30, gap_penalties_1d=(-450, -50), gap_penalties_3d=(0, 3), gap_gap_score=0, gap_residue_score=0, dendrogram_file='fm00495.tree', alignment_type='tree', # If 'progresive', the tree is not # computed and all structues will be # aligned sequentially to the first feature_weights=weights, # For a multiple sequence alignment only # the first feature needs to be non-zero improve_alignment=True, fit=True, write_fit=write_fit, write_whole_pdb=whole, output='ALIGNMENT QUALITY')

aln.write(file='achbpsPentamer.pap', alignment_format='PAP') aln.write(file='achbpsPentamer.ali', alignment_format='PIR')

aln.salign(rms_cutoffs=(1.0, 6., 60, 60, 15, 60, 60, 60, 60, 60, 60), normalize_pp_scores=False, rr_file='$(LIB)/as1.sim.mat', overhang=30, gap_penalties_1d=(-450, -50), gap_penalties_3d=(0, 3), gap_gap_score=0, gap_residue_score=0, dendrogram_file='1is3A.tree', alignment_type='progressive', feature_weights=[0]*6, improve_alignment=False, fit=False, write_fit=True, write_whole_pdb=False, output='QUALITY') ********************************************************************************** the only change that I made from the script that worked on the single subunits was to change the "model_segment" parameters from "('FIRST:'+chain, 'LAST:'+chain)" to "('FIRST:@, LAST:'))". I couldn't find anything in the Online manual concerning the arguments on the line before (for (code,chain) in.....)- should I have replaced chain "A" with something else to read the entire set of chains?

Thanks for whatever help you can provide. I am sure that as I get deeper into things that I'll have more questions- hopefully not so basic.

Mike White