DNA damage and mutagenesis of lambda phage induced by gamma-rays

Area of Science:

• Molecular Biology
• Radiation Biology
• Genetics

Background:

• Gamma irradiation induces DNA damage, including double-strand breaks (dsb), single-strand breaks (ssb), and alkali-labile sites (als).
• The biological consequences of DNA damage depend on its type and cellular context.

Purpose of the Study:

• To investigate the relationship between radiation-induced DNA damage and mutagenesis in lambda phage.
• To compare the effects of gamma irradiation on DNA within phage particles versus in aqueous solution.

Main Methods:

• Lambda phage DNA was gamma-irradiated in aqueous solution and within phage particles.
• DNA damage (dsb, ssb, als) was quantified.
• Mutagenesis was assessed in SOS-induced host cells using cI or cII cistron mutations.
• Infectivity loss was correlated with DNA structural damage.

Main Results:

• In vitro irradiated DNA showed more minor damage (ssb, als) per lethal hit compared to irradiated phage suspensions.
• Mutagenesis in packaged, irradiated DNA followed second-order kinetics, requiring two pre-mutational events.
• Mutagenesis in bacteria-free phage suspensions followed single-hit kinetics.
• Minor lesions, particularly ssb and als, were the primary drivers of increased mutation rates in packaged DNA.
• Clustered DNA damage may enhance mutagenesis in phage suspensions but is absent in packaged DNA.
• All investigated lesions contributed to biological inactivation, with dsb being the major lethal event.

Conclusions:

• The packaging of DNA within lambda phage influences the type and biological consequence of gamma-ray-induced damage.
• Minor DNA lesions play a significant role in mutagenesis within phage particles.
• Major lesions like double-strand breaks are critical for phage inactivation.