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Distinct roles of yeast MEC and RAD checkpoint genes in transcriptional induction after DNA damage and implications
1Molecular and Cellular Biology Department, University of Arizona, Tucson 85721, USA.
Abstract:
In eukaryotic cells, checkpoint genes cause arrest of cell division when DNA is damaged or when DNA replication is blocked. In this study of budding yeast checkpoint genes, we identify and characterize another role for these checkpoint genes after DNA damage-transcriptional induction of genes. We found that three checkpoint genes (of six genes tested) have strong and distinct roles in transcriptional induction in four distinct pathways of regulation (each defined by induction of specific genes). MEC1 mediates the response in three transcriptional pathways, RAD53 mediates two of these pathways, and RAD17 mediates but a single pathway. The three other checkpoint genes (including RAD9) have small (twofold) but significant roles in transcriptional induction in all pathways. One of the pathways that we identify here leads to induction of MEC1 and RAD53 checkpoint genes themselves. This suggests a positive feedback circuit that may increase the cell's ability to respond to DNA damage. We make two primary conclusions from these studies. First, MEC1 appears to be the key regulator because it is required for all responses (both transcriptional and cell cycle arrest), while other genes serve only a subset of these responses. Second, the two types of responses, transcriptional induction and cell cycle arrest, appear distinct because both require MEC1 yet only cell cycle arrest requires RAD9. These and other results were used to formulate a working model of checkpoint gene function that accounts for roles of different checkpoint genes in different responses and after different types of damage. The conclusion that the yeast MEC1 gene is a key regulator also has implications for the role of a putative human homologue, the ATM gene.
Insights
Budding yeast checkpoint genes regulate cell division and gene transcription after DNA damage. MEC1 is identified as a key regulator, controlling both cell cycle arrest and transcriptional induction pathways.
Area of Science:
- Cell Biology
- Molecular Biology
- Genetics
Background:
- Eukaryotic cells possess checkpoint genes that halt cell division upon DNA damage or replication blocks.
- The precise roles of these checkpoint genes in regulating gene expression post-DNA damage are not fully elucidated.
Purpose of the Study:
- To investigate the role of budding yeast checkpoint genes in transcriptional induction following DNA damage.
- To characterize the specific pathways and regulatory roles of key checkpoint genes in gene expression.
Main Methods:
- Systematic analysis of six budding yeast checkpoint genes.
- Identification and characterization of distinct transcriptional induction pathways regulated by checkpoint genes.
Main Results:
- Three checkpoint genes (MEC1, RAD53, RAD17) exhibit distinct roles in transcriptional induction across four regulatory pathways.
- MEC1 is crucial for three pathways, RAD53 for two, and RAD17 for one.
- A positive feedback loop was identified where MEC1 and RAD53 induce their own expression, potentially enhancing DNA damage response.
Conclusions:
- MEC1 acts as a master regulator, essential for both transcriptional induction and cell cycle arrest.
- Transcriptional induction and cell cycle arrest are distinct responses, both requiring MEC1 but only cell cycle arrest necessitating RAD9.
- A model for checkpoint gene function is proposed, highlighting differential roles in response to DNA damage, with implications for the human ATM gene homolog.