text: user4289: I recently starting studying bioinformatics and have a question. I need to build a model of protein using Swiss-Model. First, I need to download a protein record from PDB (for example, 2HZI), then I must open PDB file using simple text editor. I know this usually requires biopython, but i don't use it yet. Now I'm trying to study how to build a model.
  Swiss-model needs only one chain to build model, and I remove from file all extra information like AUTHOR,REMARK,HETATM etc. But Swiss-model still gives an error: "Sequence String contains illegal characters. Only letters and gaps allowed."
  
  user48: As explained in the website the data introduced must be:
  
  Format must be FASTA, Clustal, plain string, or a valid UniProtKB AC
  
  So you need to paste just the protein sequence. Without seeing the data you paste I would guess that you don't use a valid plain string.
  As Jonathan Moore explains below a FASTA format is:
  >SEQUENCE_1 
  MTEITAAMVKELRESTGAGMMDCKNALSETNGDFDKAVQLLREKGLGKAAKKADRLAAEG
  LVSVKVSDDFTIAAMRPSYLSYEDLDMTFVENEYKALVAELEKENEERRRLKDPNKPEHK
  IPQFASRKQLSDAILKEAEEKIKEELKAQGKPEKIWDNIIPGKMNSFIADNSQLDSKLTL
  MGQFYVMDDKKTVEQVIAEKEKEFGGKIKIVEFICFEVGEGLEKKTEDFAAEVAAQL
  
  (breaking the sequence in several lines is optional but usually done fore easy reading)
  
original_text: 4289: <p>I recently starting studying bioinformatics and have a question. I need to build a model of protein using <a href="https://swissmodel.expasy.org/interactive#structure" rel="nofollow noreferrer">Swiss-Model</a>. First, I need to download a protein record from PDB (for example, 2HZI), then I must open PDB file using simple text editor. I know this usually requires biopython, but i don't use it yet. Now I'm trying to study how to build a model.</p>
  
  <p>Swiss-model needs only one chain to build model, and I remove from file all extra information like AUTHOR,REMARK,HETATM etc. But Swiss-model still gives an error: "Sequence String contains illegal characters. Only letters and gaps allowed."</p>
   48: <p>As explained in the website the data introduced must be:</p>
  
  <blockquote>
    <p>Format must be FASTA, Clustal, plain string, or a valid UniProtKB AC</p>
  </blockquote>
  
  <p>So you need to paste just the protein sequence. Without seeing the data you paste I would guess that you don't use a valid plain string.</p>
  
  <p>As Jonathan Moore explains below a FASTA format is:</p>
  
  <pre><code>&gt;SEQUENCE_1 
  MTEITAAMVKELRESTGAGMMDCKNALSETNGDFDKAVQLLREKGLGKAAKKADRLAAEG
  LVSVKVSDDFTIAAMRPSYLSYEDLDMTFVENEYKALVAELEKENEERRRLKDPNKPEHK
  IPQFASRKQLSDAILKEAEEKIKEELKAQGKPEKIWDNIIPGKMNSFIADNSQLDSKLTL
  MGQFYVMDDKKTVEQVIAEKEKEFGGKIKIVEFICFEVGEGLEKKTEDFAAEVAAQL
  </code></pre>
  
  <p>(breaking the sequence in several lines is optional but usually done fore easy reading)</p>
  