REVIEW ARTICLE Jela Brozmanova´ Æ Viera Vlcˇkova´ Æ Miroslav Chovanec How heterologously expressed Escherichia coli genes contribute to understanding DNA repair processes in Saccharomyces cerevisiae Received: 16 July 2004 / Revised: 13 September 2004 / Accepted: 18 September 2004 / Published online: 13 November 2004 Ó Springer-Verlag 2004 Abstract DNA-damaging agents constantly challenge cellular DNA; and efficient DNA repair is therefore essential to maintain genome stability and cell viability. Several DNA repair mechanisms have evolved and these have been shown to be highly conserved from bacteria to man. DNA repair studies were originally initiated in very simple organisms such as Escherichia coli and Saccharomyces cerevisiae, bacteria being the best understood organism to date. As a consequence, bacte- rial DNA repair genes encoding proteins with well characterized functions have been transferred into higher organisms in order to increase repair capacity, or to complement repair defects, in heterologous cells. While indicating the contribution of these repair func- tions to protection against the genotoxic effects of DNA- damaging agents, heterologous expression studies also highlighted the role of the DNA lesions that are sub- strates for such processes. In addition, bacterial DNA repair-like functions could be identified in higher organisms using this approach. We heterologously expressed three well characterized E. coli repair genes in S. cerevisiae cells of different genetic backgrounds: (1) the ada gene encoding O 6 -methylguanine DNA-meth- yltransferase, a protein involved in the repair of alkyl- ation damage to DNA, (2) the recA gene encoding the main recombinase in E. coli and (3) the nth gene, the product of which (endonuclease III) is responsible for the repair of oxidative base damage. Here, we summa- rize our results and indicate the possible implications they have for a better understanding of particular DNA repair processes in S. cerevisiae. Keywords DNA repair Æ Heterologous expression Æ Saccharomyces cerevisiae Æ Escherichia coli Introduction The integrity of DNA inside cells is constantly being challenged by endogenous and exogenous DNA-dam- aging agents. The forms of DNA damage inflicted are many and include single- and double-strand breaks (SSB, DSB), chemically modified bases, abasic sites, in- ter- and intra-strand cross-links and mismatched base pairs. To maintain the integrity of the genome, living organisms have evolved a variety of systems that rec- ognize and repair different forms of DNA damage. The field of DNA repair has made considerable progress over the past 40 years. It has become evident that DNA repair is tightly connected with basic cellular processes, such as transcription and replication. Defects in DNA repair pathways provide the molecular basis of genetic diseases associated with sensitivity to DNA-damaging agents and, in multicellular organisms, can initiate events that result in cancer (Friedberg 2000; Hoeijmak- ers 2001). The lower eukaryotic organism, the budding yeast Saccharomyces cerevisiae, has already proven to be a powerful eukaryotic model system for DNA repair studies on a molecular and cellular level. The results obtained using S. cerevisiae led in many cases to the discovery of several important repair phenomena and pathways and turned them into highly relevant areas of investigation in human biology and diseases (Game 2000; Resnick and Cox 2000). Systematic research of mutagen–cell interaction in S. cerevisiae led to the discovery of great number of genetic loci with a function in DNA repair. Yeast mu- tants originally isolated by virtue of their radiation Communicated by S. Hohmann J. Brozmanova´ (&) Æ M. Chovanec Laboratory of Molecular Genetics, Cancer Research Institute, Vla´rska 7, 833 91 Bratislava, Slovak Republic E-mail: jela.brozmanova@savba.sk Tel.: +421-2-59327333 Fax: +421-2-59327350 V. Vlcˇkova´ Faculty of Natural Sciences, Department of Genetics, Comenius University, 842 15 Bratislava, Slovak Republic Curr Genet (2004) 46: 317–330 DOI 10.1007/s00294-004-0536-2