Hi Shuxiang,
You've touched a subtle point in the labeling of residues (nucleotides) in mmCIF vs. PDB. Using PDB entry 3mgp, as you used, as an example, an excerpt for the corresponding PDB and mmCIF files (all downloaded from RCSB PDB) for I.DA.-73 is as below:
# PDB format
ATOM 6169 O5' DA I -73 2.638 0.163 93.308 1.00166.52 O
ATOM 6170 C5' DA I -73 3.279 0.178 94.579 1.00166.78 C
ATOM 6171 C4' DA I -73 3.645 -1.223 95.042 1.00167.01 C
ATOM 6172 O4' DA I -73 2.489 -2.096 95.012 1.00167.37 O
ATOM 6173 C3' DA I -73 4.650 -1.969 94.180 1.00166.94 C
ATOM 6174 O3' DA I -73 5.972 -1.523 94.462 1.00166.58 O
ATOM 6175 C2' DA I -73 4.428 -3.410 94.635 1.00167.20 C
ATOM 6176 C1' DA I -73 2.941 -3.442 94.998 1.00167.53 C
ATOM 6177 N9 DA I -73 2.097 -4.257 94.106 1.00167.70 N
ATOM 6178 C8 DA I -73 0.995 -3.832 93.410 1.00167.66 C
#mmCIF:
ATOM 6161 O "O5'" . DA I 5 1 ? 2.638 0.163 93.308 1.00 166.52 ? -73 DA I "O5'" 1
ATOM 6162 C "C5'" . DA I 5 1 ? 3.279 0.178 94.579 1.00 166.78 ? -73 DA I "C5'" 1
ATOM 6163 C "C4'" . DA I 5 1 ? 3.645 -1.223 95.042 1.00 167.01 ? -73 DA I "C4'" 1
ATOM 6164 O "O4'" . DA I 5 1 ? 2.489 -2.096 95.012 1.00 167.37 ? -73 DA I "O4'" 1
ATOM 6165 C "C3'" . DA I 5 1 ? 4.650 -1.969 94.180 1.00 166.94 ? -73 DA I "C3'" 1
ATOM 6166 O "O3'" . DA I 5 1 ? 5.972 -1.523 94.462 1.00 166.58 ? -73 DA I "O3'" 1
ATOM 6167 C "C2'" . DA I 5 1 ? 4.428 -3.410 94.635 1.00 167.20 ? -73 DA I "C2'" 1
ATOM 6168 C "C1'" . DA I 5 1 ? 2.941 -3.442 94.998 1.00 167.53 ? -73 DA I "C1'" 1
ATOM 6169 N N9 . DA I 5 1 ? 2.097 -4.257 94.106 1.00 167.70 ? -73 DA I N9 1
ATOM 6170 C C8 . DA I 5 1 ? 0.995 -3.832 93.410 1.00 167.66 ? -73 DA I C8 1
As noted in the mmCIF header, the sequence number "-73" matches "_atom_site.auth_seq_id", and number "1" matches "_atom_site.label_seq_id". Since the corresponding PDB entry uses
_atom_site.auth_seq_id (-73), DSSR follows that convention.
DSSR currently has
no option to employ the labeling "_atom_site.label_seq_id" while "_atom_site.auth_seq_id" exists.
Best regards,
Xiang-Jun