1. Laboratory of DNA Replication and Genome Stability, Institute of Biochemistry and Biophysics, Polish Academy of Sciences , Warsaw 02-106, Poland
2. Department of Medical Biochemistry and Cell Biology, University of Gothenburg , Gothenburg 40530, Sweden
3. Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health , Bethesda , MD 20892-3371 , USA