diff --git a/projects/human-heterodimers-w-crosslinks/translate2modelcif.py b/projects/human-heterodimers-w-crosslinks/translate2modelcif.py
index df86631e37023797bcfb18f79d4e0cc1a49c979e..4f5dbb70c4e25a5d7c4264c2e27a8a97b25833ab 100755
--- a/projects/human-heterodimers-w-crosslinks/translate2modelcif.py
+++ b/projects/human-heterodimers-w-crosslinks/translate2modelcif.py
@@ -228,6 +228,11 @@ def _abort_msg(msg, exit_code=1):
     sys.exit(exit_code)
 
 
+def _warn_msg(msg):
+    """Write a warning message to stdout."""
+    print(f"WARNING: {msg}")
+
+
 def _check_file(file_path):
     """Make sure a file exists and is actually a file."""
     if not os.path.exists(file_path):
@@ -292,9 +297,8 @@ def _parse_colabfold_config(cnfg_file):
         use_mmseqs = False
         use_msa = False
     elif cf_config["msa_mode"] == "custom":
-        print(
-            "WARNING: Custom MSA mode used. Not clear from config what to do "
-            + "here!"
+        _warn_msg(
+            "Custom MSA mode used. Not clear from config what to do here!"
         )
         seq_dbs = []
         use_mmseqs = False
@@ -336,9 +340,9 @@ def _parse_colabfold_config(cnfg_file):
     else:
         mdl_description += ", without model relaxation"
     if cf_config["use_templates"]:
-        print(
-            "WARNING: ColabFold may use PDB70 or custom templates. "
-            "Not clear from config!"
+        _warn_msg(
+            "ColabFold may use PDB70 or custom templates. Not clear "
+            + "from config!"
         )
         mdl_description += ", using templates"
     else:
@@ -553,12 +557,22 @@ def _get_sequence(chn):
 
 def _check_sequence(up_ac, sequence):
     """Verify sequence to only contain standard olc."""
-    for res in sequence:
+    ns_aa_pos = []  # positions of non-standard amino acids
+    for i, res in enumerate(sequence):
         if res not in "ACDEFGHIKLMNPQRSTVWY":
+            if res == "U":
+                _warn_msg(
+                    f"Selenocysteine found at position {i+1} of entry "
+                    + f"'{up_ac}', this residue may be missing in the "
+                    + "model."
+                )
+                ns_aa_pos.append(i)
+                continue
             raise RuntimeError(
                 "Non-standard aa found in UniProtKB sequence "
-                + f"for entry '{up_ac}': {res}"
+                + f"for entry '{up_ac}': {res}, position {i+1}"
             )
+    return ns_aa_pos
 
 
 def _get_n_parse_up_entry(up_ac, up_url):
@@ -626,7 +640,11 @@ def _get_n_parse_up_entry(up_ac, up_url):
     data["up_isoform"] = None
 
     if "up_gn" not in data:
-        _abort_msg(f"No gene name found for UniProtKB entry '{up_ac}'.")
+        _warn_msg(
+            f"No gene name found for UniProtKB entry '{up_ac}', using "
+            + "UniProtKB AC instead."
+        )
+        data["up_gn"] = up_ac
     if "up_last_mod" not in data:
         _abort_msg(f"No sequence version found for UniProtKB entry '{up_ac}'.")
     if "up_crc64" not in data:
@@ -640,7 +658,7 @@ def _get_n_parse_up_entry(up_ac, up_url):
             + f"UniProtKB entry '{up_ac}': {data['up_seqlen']} != "
             + f"{len(data['up_sequence'])}"
         )
-    _check_sequence(data["up_ac"], data["up_sequence"])
+    data["up_ns_aa"] = _check_sequence(data["up_ac"], data["up_sequence"])
 
     if "up_id" not in data:
         _abort_msg(f"No ID found for UniProtKB entry '{up_ac}'.")
@@ -668,10 +686,24 @@ def _fetch_unisave_entry(up_ac, version):
     )
 
 
+def _cmp_sequences(mdl, upkb, ns_aa_pos):
+    """Compare sequence while paying attention on non-standard amino acids."""
+    # We add a U to the sequence when necessary. AF2 does not model it. The PDB
+    # has selenocysteine as canonical aa, see PDB entry 7Z0T.
+    for pos in ns_aa_pos:
+        if mdl[pos] != "-":
+            _abort_msg(
+                f"Position {pos+1} of non-canonical amino acid should be "
+                "a gap!"
+            )
+        mdl = mdl[0:pos] + "U" + mdl[pos + 1 :]
+    return mdl == upkb
+
+
 def _get_upkb_for_sequence(sqe, up_ac):
     """Get UniProtKB entry data for given sequence."""
     up_data = _fetch_upkb_entry(up_ac)
-    while sqe != up_data["up_sequence"]:
+    while not _cmp_sequences(sqe, up_data["up_sequence"], up_data["up_ns_aa"]):
         if up_data["up_entry_version"] > 1:
             up_data = _fetch_unisave_entry(
                 up_ac, up_data["up_entry_version"] - 1
@@ -732,7 +764,10 @@ def _get_modelcif_entities(target_ents, source, asym_units, system):
     """Create ModelCIF entities and asymmetric units."""
     for cif_ent in target_ents:
         mdlcif_ent = modelcif.Entity(
-            cif_ent["pdb_sequence"],
+            # Use up_sequence above pdb_sequence as it contains no gaps but
+            # otherwise is equal to the pdb_sequence. Gaps in pdb_sequence
+            # originate from missing residues in the model.
+            cif_ent["up_sequence"],
             description=cif_ent["description"],
             source=source,
             references=[
@@ -1111,3 +1146,5 @@ def _main():
 
 if __name__ == "__main__":
     _main()
+
+#  LocalWords:  aa pdb