The stringent and relaxed phenomena in Saccharomyces cerevisiae

Current understanding of RNA metabolism in yeast remains incomplete, particularly regarding how amino acid availability influences RNA synthesis. Prior research has shown that amino acid starvation affects RNA synthesis in prokaryotes through stringent responses, but less is known about eukaryotic systems like Saccharomyces cerevisiae. While established knowledge includes the role of transcription in RNA synthesis, the specific effects of amino acid starvation on different RNA species remain unclear. No prior work had resolved how transcription rates differ across RNA types during nutrient stress. This gap motivated further investigation into the coordination of RNA synthesis under starvation. The role of cycloheximide in modulating RNA metabolism is also not fully understood. This uncertainty drove the need to examine whether transcriptional responses vary across RNA species. The lack of data on salvage pathways for nucleotide synthesis in yeast created a need for detailed analysis. The absence of clear evidence on how methylation rates relate to transcription rates in yeast RNA metabolism also required clarification.

This study aimed to clarify how amino acid starvation and cycloheximide affect RNA metabolism in yeast. The specific problem addressed is the coordination of RNA synthesis across different RNA species during nutrient stress. The motivation stems from the need to understand how transcriptional regulation varies under amino acid starvation. Researchers sought to determine whether salvage pathways for nucleotide synthesis are regulated by transcription rates. The study also aimed to assess the reliability of using methionine labeling to quantify RNA synthesis. Another objective was to evaluate how cycloheximide influences RNA synthesis in starved and non-starved conditions. The researchers focused on the differential effects of cycloheximide on various RNA species. The study aimed to identify whether the observed effects are unique to yeast or represent a broader eukaryotic phenomenon.

The study used amino acid starvation and cycloheximide treatment to examine RNA metabolism in yeast cells and spheroplasts. Researchers measured uridine phosphorylation, rRNA methylation, and the biosynthesis of 35 S, 4 S, and 5 S RNA species. They applied [methyl-3H]methionine labeling to assess RNA synthesis rates. The experimental design included comparing RNA synthesis in starved and non-starved conditions. Researchers tracked changes in uridine incorporation into RNA over time. They analyzed the rate of rRNA methylation independently of transcription rates. Cycloheximide was added at low concentrations to observe its effects on RNA synthesis. The study also measured RNA decay rates to determine the drug’s impact on transcription.

Amino acid starvation significantly inhibits uridine phosphorylation for RNA synthesis compared to other metabolic processes. This suggests a salvage pathway for UMP and CMP synthesis is regulated by transcription rates. The rate of rRNA methylation is not coupled with transcription rates, making methionine labeling unreliable for quantifying RNA synthesis. 35 S RNA synthesis ceases immediately after amino acid starvation begins. At later stages, 4 S and 5 S RNA synthesis also declines, indicating a time-dependent response. Cycloheximide at low doses increases uridine incorporation into RNA in starved spheroplasts. This effect is stronger for 4 S and 5 S RNA than for 35 S RNA. Cycloheximide does not alter the decay rate of 35 S RNA in starved cells but inhibits transcription in non-starved conditions.

The study shows that amino acid starvation disrupts RNA synthesis in a time-dependent manner across different RNA species. The salvage pathway for nucleotide synthesis appears to be regulated by transcription rates and may be localized in the nucleus. Methionine labeling is an unreliable method for quantifying RNA synthesis due to the lack of coupling between methylation and transcription. Cycloheximide increases uridine incorporation into RNA in starved cells but does not affect RNA decay rates. The drug’s effect on transcription varies depending on the RNA species and starvation status. The observed opposite effects of cycloheximide in starved and non-starved conditions suggest a unique feature of eukaryotic RNA metabolism. These findings imply that transcriptional regulation in yeast is more complex than previously assumed. The results highlight the need for further research into the mechanisms underlying RNA synthesis coordination.