Altered S‐AdenosylMethionine availability impacts dNTP pools in Saccharomyces cerevisiae

Saccharomyces cerevisiae has long been used as a model organism to study genome instability. The SAM1 and SAM2 genes encode AdoMet synthetases, which generate S‐AdenosylMethionine (AdoMet) from Methionine (Met) and ATP. Previous work from our group has shown that deletions of the SAM1 and SAM2 genes cause changes to AdoMet levels and impact genome instability in opposite manners. AdoMet is a key product of methionine metabolism and the major methyl donor for methylation events of proteins, RNAs, small molecules, and lipids. The methyl cycle is interrelated to the folate cycle which is involved in de novo synthesis of purine and pyrimidine deoxyribonucleotides (dATP, dTTP, dCTP, and dGTP). AdoMet also plays a role in polyamine production, essential for cell growth and used in detoxification of reactive oxygen species (ROS) and maintenance of the redox status in cells. This is also impacted by the methyl cycle's role in production of glutathione, another ROS scavenger and cellular protectant. We show here that sam2∆/sam2∆ cells, previously characterized with lower levels of AdoMet and higher genome instability, have a higher level of each dNTP (except dTTP), contributing to a higher overall dNTP pool level when compared to wildtype. Unchecked, these increased levels can lead to multiple types of DNA damage which could account for the genome instability increases in these cells. sam1∆/sam1∆ cells have increased genome stability and AdoMet and show lowered γ‐glutamyl‐l‐cysteinyl‐glycine levels. Conversely, sam2∆/sam2∆ cells have decreased genome stability and AdoMet and show lowered ATP levels but increased overall dNTP pools. Changes in dNTP levels are known to decrease genome stability, linking these changes in sam2‐deficient cells. Black = no change, Gray = unmeasured, Blue = decreased, Tan = increased. Take‐away SAM gene loss alters AdoMet levels and genome instability in opposite manners. sam1∆/sam1∆ cells have less reduced GSH and altered dATP, dCTP, and dTTP. sam1 results explain previously seen sensitivity to hydroxyurea. sam2∆/sam2∆ cells have less ATP and increased dNTPs. sam2 results give a mechanistic underpinning to observed genome instability.