The Role of Clays in Shielding DNA against X-Ray Radiation: Possible Implications on the origin of life Angela Ciaravella F. Scappini (2), M. Franchi (3), E. Gallori (3), C. Cecchi-Pestellini (4), M. Barbera (1), R. Candia (1), G. Micela (1) (1)INAF – Osservatorio Astronomico di Palermo, Italy (2)ISMN –CNR, Bologna, Italy (3)Dipartimento di Biologia Animale e Genetica, Univ. di Firenze, Italy (4)Dipartimento di Fisica, Univ di Lecce, Italy Firenze 28/02 – 1/03/05

First evidence of life on the Earth 3.8 × 10 9 yr Earth Atmosphere : a big unknow, very little screening from Sun radiation Conditions on the Early Earth Early X-ray Sun: more active, hard and bright 3 × (0.1 keV) = erg/sec 5 × (0.2 keV) Yohkoh-SXT 3-40 Å band 1-10 keV band: the photon flux today is ~10 -3 the flux at the age of Pleiades min max How and under which conditions life was created?

DNA Irradiation Free DNA type B Clay Adsorbed DNA type A 34 Å per turn B Å per turn A Why DNA? DNA is already life An easy and well tested method to estimate damage We irradiate free and clay absorbed DNA from Bacillus Subtilis CLAYS: Montmorillonite Na 0.2 Ca 0.1 Al 2 Si 4 O 10 (OH) 2 (H 2 O) 10 Kaolinite Al 2 Si 2 O 5 (OH) 4

Vacuum tight container X-ray, UV, Vis eV ( A). 17 m stainless-steel vacum beam line class 1000 clean_room (Barbera et al 1999). The XACT Facility: Al Ti Cu Flux (erg sec -1 cm -2 ) Line (keV ) DNA X-Ray Irradiation Irradiation Dose : × 10 4 erg Exposure Time : 2 m - 16 h minimum 3 × maximum large flares The Sun today (1.5 –12.4 keV): DNA Samples: Free 10μg DNA l of H 2 O Clay Adsorbed 10μg DNA + 2mg Clay l of H 2 O

DNA Damage Evaluation The integrity of DNA molecules is estimated by transformation experiments : efficiency of irradiated DNA to transform competent cell in a bacterial culture Comparing Ftf with Ftf 0 the damage is evaluated Typical errors on Ftf are 20 % The transformation frequence is: Transformation frequence for non irradiated DNA

Results and Conclusions I *** Free DNA is severely damaged by X-rays and the damage depends on the energy dose rather than the hardness of radiation Clay Adsorbed DNA is resistent to the X-ray irradiation Can clays shield DNA against X-rays? Diluted clay is much more transparent than H 2 O to X-rays The more compact configuration (A) of clay adsorbed DNA binding to the substrate by electrostatic and/or hydrogen bonds can play protective role

Results and Conclusions II Are X-rays directly responsible for DNA damage? Num X photons (Cu 5 × 10 4 erg) 4 × Num H 2 O molecules 5 × Num DNA molecules 4 × Secondary UV UV irradiation of free and clay adsorbed DNA give similar results (Scappini et al 2004) 2.5 mm 1 mm 0.2 mm 0.01 mm Are clays essential in protecting the basic building blocks of life as well ? DNA adsorbed on clays do survive X-rays and UV photodegradation