A chicken repetitive DNA sequence that is highly sensitive to single-strand specific endonucleases

Area of Science:

• Genetics
• Molecular Biology
• Biochemistry

Background:

• Repetitive DNA sequences are common in eukaryotic genomes.
• The function and properties of many repetitive elements remain poorly understood.
• Specific DNA-binding proteins and enzymes can interact with repetitive DNA structures.

Purpose of the Study:

• To characterize a specific repetitive DNA sequence found in the chicken genome.
• To investigate the susceptibility of this sequence to single-strand specific endonucleases.
• To understand the enzymatic requirements for cleaving this repetitive DNA.

Main Methods:

• Detection and characterization of a tandemly repeated 5-mer DNA sequence (AGAGG) in chicken genomic DNA.
• Analysis of the repetitive sequence's copy number per genome.
• Enzymatic assays using single-strand specific endonucleases from Aspergillus oryzae (S1), mung bean, and Neurospora crassa.
• Investigation of enzyme cleavage activity under varying pH and ionic strength conditions.
• Requirement of a supercoiled substrate for endonucleolytic cutting.

Main Results:

• A DNA sequence composed of the 5-mer AGAGG repeated 32 times was identified in a chicken genomic clone.
• This sequence is present in approximately 2000 copies within the chicken genome.
• The AGAGG repeat was highly sensitive to single-strand specific endonucleases from Aspergillus oryzae (S1) and mung bean.
• Cleavage by Neurospora crassa endonuclease was pH-dependent, occurring only below pH 5.5.
• Enzymatic cleavage required a supercoiled DNA substrate and was independent of ionic strength.

Conclusions:

• The repetitive AGAGG sequence exhibits unique susceptibility to specific single-strand specific endonucleases.
• The enzymatic cleavage mechanism is dependent on DNA supercoiling and pH (for N. crassa).
• These findings provide insights into the biochemical properties of repetitive DNA elements in the chicken genome.