Abstract Homologous recombination in Saccharomyces cerevisiae and other organisms can be stimulated by tran- scription. Consistent with this, we find that recombination of a chromosomal ade1 allele with a plasmid-borne ADE1 ORF under the control of the GAL1 promoter increased from 6.1 × 10 –6 to 1.7 × 10 –4 when transcription of the plas- mid locus was induced by growing the cells in the pres- ence of galactose. Recombination could also be stimulated by over-expressing the Gal4 transcription factor in the presence of the GAL1-ADE1 plasmid, while culturing the cells in dextrose medium. However, when transcription of the same ORF was driven from the highly active promot- ers of the rDNA (RNA polymerase I), and ADH1 (RNA polymerase II) genes, only background levels of recombi- nation (5–10 × 10 –6 ) were observed, irrespective of the car- bon source. Recombination was found to involve integra- tion of the whole plasmid and to depend on RAD51, RAD52 and RAD54. The results indicate that increased accessibil- ity of transcriptionally active chromatin is not sufficient to cause increased rates of this kind of reciprocal exchange. Key words Ade1 · Recombination · Gal promoter · Transcription Introduction Data gleaned from a variety of systems in recent years im- plicate the process of transcription in a series of superfi- cially unrelated aspects of genome dynamics in living cells. Transcriptionally activated regions of the genome can be subject to elevated rates of mutation, repair, and recombi- nation. For example, reversion of a frame-shift mutation in the LYS2 gene of S. cerevisiae was stimulated 30-fold in a strain that actively transcribed the mutant allele, as compared to a strain not efficiently expressing that locus (Datta and Jinks-Robertson 1995). Several yeast nucle- otide excision repair proteins, including Rad3p, Ssl1p and Tfb1p, are also essential components of the RNA polymer- ase-II general transcription factor TFIIH, and a higher-or- der repair complex involving TFIIH, Rad14p and Rad23p apparently forms subsequent to UV damage of DNA, pro- viding a glimpse of a mechanistic link between transcrip- tion and DNA repair (Guzder et al. 1995; Wang et al. 1995). Human TFIIH has been shown to contain the ERCC3 DNA helicase implicated in the repair disorder Xeroderma Pig- mentosum (Drapkin et al. 1994). As for recombination, excision of exogenous DNA between spaced duplications of the GAL1 gene was ele- vated 15-fold in a gal80 background (Thomas and Roth- stein 1989). A genetic element known as HOT1 causes lo- cal increased rates of mitotic recombination when moved to ectopic sites in the yeast genome (Keil and Roeder 1984). HOT1 sequences correspond to the promoter region of the rDNA locus, and the RNA polymerase-I transcriptional ac- tivity initiated at this element is required for the increase in recombination (Voelkel-Meiman et al. 1987). Nevo- Caspi and Kupiec (1994) showed that mitotic recombina- tion of marked Ty elements was increased when transcrip- tion of the acceptor locus controlled by the GAL1 promoter was induced. Attempts have been made to develop models to explain the observed influence of transcription on recombination, and the proposals made to-date may be divided into two classes (Thomas and Rothstein 1989; Nevo-Caspi and Ku- piec 1994). In one class, attention is focussed on changes in the high-level structure of chromatin. Such alterations would either provoke damage of the DNA leading to rec- ombinational repair, or would allow easier access to an- other factor that stimulates recombination, perhaps a nu- clease or an enzyme catalysing strand transfer, such as Rad51p (Grimm et al. 1991). In the other class, a factor normally associated with the transcription complex would also have recombination-promoting activity. By analogy with the function of Rad3p as both an excision repair fac- Curr Genet (1996) 30: 381 – 388 © Springer-Verlag 1996 Received: 2 May / 26 July 1996 John Bratty · Gerardo Ferbeyre · Carmela Molinaro · Robert Cedergren Stimulation of mitotic recombination upon transcription from the yeast GAL1 promoter but not from other RNA polymerase I, II and III promoters ORIGINAL PAPER J. Bratty · G. Ferbeyre · C. Molinaro · R. Cedergren () Département de biochimie, Université de Montréal, Montréal, H3C 3J7, Canada Communicated by A. Nicolas