4774 Nucleic Acids Research, 2005, Vol. 33, No. 15 a novel eukaryotic DNA polymerase with a potential role in meiosis. J. Mol. Biol., 301, 851–867. 63. Nick McElhinny,S.A. and Ramsden,D.A. (2004) Sibling rivalry: competition between Pol X family members in V(D)J recombination and general double strand break repair. Immunol. Rev., 200, 156–164. 64. Bebenek,K., Garcia-Diaz,M., Patishall,S.R. and Kunkel,T.A. (2005) Biochemical properties of Saccharomyces cerevisiae DNA polymerase IV. J. Biol. Chem., 280, 20051–20058. 65. Bonnin,A., Lazaro,J.M., Blanco,L. and Salas,M. (1999) A single tyrosine prevents insertion of ribonucleotides in the eukaryotic-type phi29 DNA polymerase. J. Mol. Biol., 290, 241–251. 66. Ferreira,M.G. and Cooper,J.P. (2004) Two modes of DNA double-strand break repair are reciprocally regulated through the fission yeast cell cycle. Genes Dev., 18, 2249–2254. 67. Karathanasis,E. and Wilson,T.E. (2002) Enhancement of Saccharomyces cerevisiae end-joining efficiency by cell growth stage but not by impairment of recombination. Genetics, 161, 1015–1027. 68. Takata,M., Sasaki,M.S., Sonoda,E., Morrison,C., Hashimoto,M., Utsumi,H., Yamaguchi-Iwai,Y., Shinohara,A. and Takeda,S. (1998) Homologous recombination and non-homologous end-joining pathways of DNA double-strand break repair have overlapping roles in the maintenance of chromosomal integrity in vertebrate cells. EMBO J., 17, 5497–5508. 69. McCormick,P.J., Danhauser,L.L., Rustum,Y.M. and Bertram,J.S. (1983) Changes in ribo- and deoxyribonucleoside triphosphate pools within the cell cycle of a synchronized mouse fibroblast cell line. Biochim. Biophys. Acta, 756, 36–40. 70. Meuth,M. (1984) The genetic consequences of nucleotide precursor pool imbalance in mammalian cells. Mutat. Res., 126, 107–112. 71. Rydberg,B. and Game,J. (2002) Excision of misincorporated ribonucleotides in DNA by RNase H (type 2) and FEN-1 in cell-free extracts. Proc. Natl Acad. Sci. USA, 99, 16654–16659. 72. Kaykov,A. and Arcangioli,B. (2004) A programmed strand-specific and modified nick in S.pombe constitutes a novel type of chromosomal imprint. Curr. Biol., 14, 1924–1928.