(a) Schematic of the exon–intron structure of the AtATM gene drawn to scale. All coding exons are represented by black boxes; the first exon, which is non-coding, by a white box. (b) Schematic of the primary structure of the AtAtm protein. PWWP, hath or PWWP domain; ATM, similarity to human Atm; rad3, rad3 domain; CC, coiled-coil domain ; Pi3k, phosphatidyl inositol-3 kinase-like domain ; C-ter, C-terminal domain characteristic of the Atm/Tor family of proteins.