Studying DNA repair means, among others, to study the temporal sequence of events immediately after DNA damage induction, i.e. the kinetics. Getting the time zero point is difficult with most techniques so far employed. The laser microbeam allows to get this starting point with sub-second accuracy. For that purpose, the laser is directed into a small region of the cell nucleus and induces there DNA double strand breaks. The recruitment of different, fluorescently  (GFP) labeled DNA repair proteins is then studied by direct observation in the microsope.

Major results are:

i) Pre-irradiation with red light protects DNA against UV damage  He-Ne laser irradiation protects B -lymphocytes from UV A induced DNA damage 2001 Rad Environ Biophys  40   77 -  82

ii) Human chromosomes with high active gene density are less prone to DNA damage than inactive chromosomes
UV A breakage sensitivity of human chromosomes as measured by COMET-FISH depends on gene density and not on chromosome size    2000 Photochem Photobiol 56 106 - 117

iii) All double strand break repair starts with the supposedly error prone non homologous end joining,  the switch to error free homologous recombination repair is possible only after approx. 1 min, when NBS1 respectively the MRN complex has bound  2009 ChemPhysChem 10, 79 - 85 see also below
 
iv) A number of drugs used in pharmacology which are not genotoxic by themselves do become so in UV irradiated rats.
Repair of Sparfloxacin Induced Photochemical DNA Damages in vitro and in vivo   2009 J Invest Dermatol 129, 699 - 704



A direct view by immunofluorescent comet assay (IFCA) of DNA damage induced by nicking and cutting enzymes,  ionizing ¹³⁷Cs radiation,
UV-A laser microbeam irradiation and the radiomimetic drug bleomycin  2009 Mutagenesis 24, 191-197

Laser Microbeams and Optical Tweezers in Ageing Research   PDF  2009 ChemPhysChem 10, 79 - 85


Background Information
Comet-assay and Comet-FISH (Teaching text)                                                                                                                   IFCA – Immunofluorescent Comet Assay (Poster)

Uncovering the earliest steps of DNA double strand break repair (Poster)                                                                       Laser microbeam induced DNA damages and repair (Poster)

UV-A Induced DNA Damage (Teaching Text)                                 DNA Double Strand Repair (Teaching Text)                      Intrinsic Oxidative DNA Damages (Teaching Text)