5'-exonuclease

An enzyme that cleaves nucleotides from the end of a DNA or RNA strand

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5'-exonuclease is an enzyme that cleaves nucleotides one at a time from the 5' end of a polynucleotide chain. This type of enzyme is crucial in various biological processes, including DNA replication, DNA repair, and RNA processing.

Function

5'-exonucleases play a vital role in the maintenance and integrity of genetic information. During DNA replication, these enzymes are involved in the removal of RNA primers from the Okazaki fragments on the lagging strand. This process is essential for the synthesis of a continuous DNA strand.

In DNA repair, 5'-exonucleases are involved in the excision of damaged or mismatched nucleotides, allowing for the correction of errors and the prevention of mutations. They are also involved in the processing of double-strand breaks and the removal of nucleotide excision products.

Mechanism

5'-exonucleases function by hydrolyzing the phosphodiester bond at the 5' end of a nucleic acid chain. This enzymatic activity requires the presence of divalent metal ions, such as magnesium or manganese, which are essential for catalysis. The enzyme binds to the substrate and catalyzes the removal of nucleotides in a sequential manner, releasing mononucleotides.

Examples

One well-known example of a 5'-exonuclease is the DNA polymerase I from Escherichia coli, which possesses both polymerase and 5'-exonuclease activities. This enzyme is responsible for the removal of RNA primers during DNA replication and the filling in of the resulting gaps with DNA.

Another example is the Exonuclease T from E. coli, which is involved in the degradation of RNA molecules.

Applications

5'-exonucleases have important applications in molecular biology and biotechnology. They are used in techniques such as polymerase chain reaction (PCR) to remove unwanted nucleic acid sequences and in genetic engineering to manipulate DNA sequences.

Also see

• 3'-exonuclease
• Endonuclease
• DNA polymerase
• RNA polymerase
• Nuclease