Colicin E2 is DNA endonuclease.

Area of Science:

• Molecular Biology
• Microbial Genetics
• Biochemistry

Background:

• Colicin E2, a bacteriocin, exhibits toxicity to sensitive bacterial strains.
• Purified colicin E2 preparations typically contain a tightly bound low-molecular-weight protein.
• Conventional purification methods yield colicin E2 that does not cleave DNA in vitro.

Purpose of the Study:

• To elucidate the enzymatic activity of colicin E2.
• To characterize the role of the associated low-molecular-weight protein.
• To understand the mechanism of colicin E2-mediated DNA cleavage and immunity.

Main Methods:

• Purification of colicin E2.
• Separation of colicin E2 from the associated low-molecular-weight protein.
• In vitro DNA cleavage assays using various DNA substrates (ColE1 hybrid plasmid, E. coli, lambda phage, chiX174 phage, SV40 DNA).
• Assessment of the inhibitory effect of the low-molecular-weight protein on DNA cleavage.

Main Results:

• Colicin E2, after removal of the low-molecular-weight protein, demonstrated potent DNA endonuclease activity in vitro.
• The separated colicin E2 retained its original in vivo killing activity.
• The low-molecular-weight protein specifically inhibited the in vitro DNA cleavage activity of colicin E2, acting as an "immunity protein".

Conclusions:

• Colicin E2 itself functions as a DNA endonuclease.
• The associated low-molecular-weight protein confers immunity by inhibiting the endonuclease activity.
• These findings explain the in vivo DNA cleavage effects and immunity mechanism in colicin E2-producing cells.