The effect of U.V.-irradiation on lambda DNA transcription

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Ultraviolet (U.V.) irradiation is known to damage DNA, potentially affecting its biological functions.
• Understanding how DNA damage impacts transcription is crucial for comprehending DNA repair mechanisms and gene expression regulation.

Purpose of the Study:

• To investigate the in vitro effects of U.V. irradiation on lambda DNA template activity in the E. coli RNA polymerase system.
• To determine if U.V. damage alters DNA initiation sites, transcription product length, and asymmetry.

Main Methods:

• In vitro transcription assays using native and U.V.-treated lambda DNA with E. coli RNA polymerase.
• Kinetic analysis of the transcription reaction.
• Hybridization studies of transcription products with lambda DNA halves (R and L).
• Incorporation of 32P-labelled nucleoside triphosphates to quantify RNA synthesis.

Main Results:

• Lambda DNA is more susceptible to U.V. damage than calf-thymus DNA, but residual transcription activity persists at high U.V. doses.
• U.V. irradiation does not appear to affect the DNA initiation sites recognized by RNA polymerase.
• Transcription products from U.V.-treated lambda DNA exhibit asymmetrical hybridization (R/L ratio of 4/1) and reduced overall hybridizability compared to native DNA.
• Transcription from U.V.-treated lambda DNA results in shorter RNA chains, suggesting premature termination.

Conclusions:

• U.V. irradiation of lambda DNA primarily impacts the elongation phase of transcription rather than initiation.
• The observed changes in transcription product length and asymmetry indicate that DNA damage can lead to altered gene expression patterns.
• RNA polymerase can still recognize initiation sites on damaged DNA, but the process of RNA synthesis is significantly impaired.