Résumé
In the yeast Saccharomyces cerevisiae, as in other eukaryotes, some regions of the genome have a much higher level of meiotic gene conversion than others. Previous deletion analysis indicated that the sequence necessary for the high level of gene conversion within the ARG4 region defined an initiation site located between positions -316 and -37 [relative to the first base pair (+1) of the ARG4 coding sequence] of the ARG4 promoter. To test whether this sequence is sufficient to promote gene conversion in a novel chromosomal context, we inverted on the chromosome various DNA fragments including the implicated region and the ARG4 coding sequence. Surprisingly, these inversions resulted in the loss of the normal recombination properties and double-strand-break formation associated with this process. By Northern analysis, we found that a transcript traverses the ARG4 initiation site in these inversion mutants but not in the wild type. When transcription through this region was prevented by a transcription terminator, the activity of the initiation site and the formation of double-strand breaks were restored. From these results and from complementary deletion analysis in the normal ARG4 orientation, we conclude that the activity of the ARG4 initiation site requires protection from transcriptional interference.