Expression of the Saccharomyces cerevisiae RAD50 gene during meiosis: steady-state transcript levels rise and fall while steady-state protein levels remain constant.

In Saccharomyces cerevisiae, the RAD50 gene is required for repair of X-ray and MMS-induced DNA damage during vegetative growth, and for synaptonemal complex formation and genetic recombination during meiosis. We show below that the RAD50 gene encodes major and minor transcripts of 4.2 and 4.6 kb in length which differ primarily at their 5' ends. Steady-state levels of both RAD50 transcripts increase coordinately during meiosis, reaching maximal levels midway through meiotic prophase, about 3 or 4 h after transfer of cells to sporulation medium. The 5' ends of the major RAD50 transcript in both meiotic and vegetative cells map to the same cluster of sites approximately 20 bp upstream of the amino-terminal ATG of the RAD50 coding sequence. We conclude that the increased RAD50 transcript level observed during meiosis does not reflect utilization of a new promoter. In contrast, steady-state levels of Rad50 protein do not increase during meiosis. Thus, changes in RAD50 transcript levels are not necessarily accompanied by commensurate changes in Rad50 protein levels. Possible explanations are considered.