Update app.py

app.py

@@ -64,6 +64,12 @@ def read_dna_sequence(dna_text, fasta_file):
         dna_sequence = dna_sequence.upper()
         warning += "\n⚠️ Note: DNA sequence was converted to uppercase (lowercase nucleotides are not supported)."
 
+    if error != "":
+        # If there was an error before, no need to check the content of the sequence. Otherwise, check that only ACGTN are used
+        for nucleotide in dna_sequence:
+            if nucleotide not in ["A", "C", "G", "T", "N"]:
+                error = "❌ The nucleotides of the DNA sequence should be either 'A', 'T', 'G', 'C' or 'N'."
+
     return dna_sequence, warning.strip(), error
 
 
@@ -148,7 +154,7 @@ with gr.Blocks(css=css) as demo:
     gr.Markdown(
         """
         # 🧬 ChatNT: A Multimodal Conversational Agent for DNA, RNA and Protein Tasks
-        [ChatNT](https://www.nature.com/articles/s42256-025-01047-1) is the first multimodal conversational agent designed with a deep understanding of biological sequences (DNA, RNA, proteins). It enables users — even those with no coding background — to interact with biological data through natural language and it generalizes across multiple biological tasks and modalities
+        [ChatNT](https://www.nature.com/articles/s42256-025-01047-1) is the first multimodal conversational agent designed with a deep understanding of biological sequences (DNA, RNA, proteins). It enables users — even those with no coding background — to interact with biological data through natural language and it generalizes across multiple biological tasks and modalities.
         
         This Hugging Face Space is powered by a [ZeroGPU](https://huggingface.co/docs/hub/en/spaces-zerogpu), which is free but **limited to 5 minutes per day per user**.
         """