Labelling of DNA & RNA can be done using:

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1. Radioactive isotopes
2. Non-Radioactive isotopes

commonly used radioactive isotopes are : ¹²⁵I, ¹⁴C ¹⁵N, ³⁵S, ³²P, etc.
Labelling can be done using 3 methods

1. Nick Translation
2. End Labelling
3. Random Primer Labelling

Nick Translation

• Rapid, easy and inexpensive method.
• Amount of DNase  I added is critical
• Reaction stopped using EDTA.
• Purification can be done either by Column chromatography or by Gel Extraction.

End Labelling

• End labelling can be done by two ways: 3’ End Labelling and 5’ End Labelling.

End Labelling

• The Selected DNA is digested with restriction enzymes to generate sticky end.

Disadvantages of Radioactive Isotope Labelling

• It is hazardous
• Require long exposure times
• Costly
• Instability due to the half life period of radioactive isotopes.

• Safe.
• Stable.
• Economical.
• More stable compared to radioactive isotope labelling.

1. Labelling with Biotinylated nucleotide
2. Labelling with HRP conjugate

Disadvantages of Non Radioactive Isotope Labelling

• Less Sensitive

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