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Functional and physical interactions of 14-3-3 proteins with novel targets upon replication stress in S. cerevisiae


Aykut, Murat. Functional and physical interactions of 14-3-3 proteins with novel targets upon replication stress in S. cerevisiae. 2015, University of Zurich, Faculty of Science.

Abstract

The integrity of DNA replication forks is important for cell viability. In replication checkpoint-deficient budding yeast, disturbances caused by DNA damaging agents possibly result in fork collapse or DNA breaks/rearrangements. Previous studies from our laboratory indicated that 14-3-3-deficient yeast cells cannot restart replication forks in response to hydroxyurea (HU) treatment. The data also indicated that in these cells ssDNA gaps accumulate behind the fork in an Exo1-dependent manner. However, while deletion of EXO1 rescued the accumulation of ssDNA gaps, it was unable to rescue HU sensitivity and the slow fork progression/restart defect of 14-3-3- deficient cells. These studies highlighted the fact that additional unknown targets of 14-3-3 proteins contribute to promote fork progression, stability and restart. From a list of established 14-3-3-interacting proteins selected in silico on the base of their involvement in DNA transactions, we attempted to identify factors that suppress fork restart upon HU-release in 14-3-3-deficient cells. We obtained evidence that Dpb3, one of the two accessory subunits of Pol ε, physically interacts with yeast 14-3-3 (Bmh1) in vivo and that deletion of DPB3 partially suppresses the HU sensitivity of 14-3-3-deficient cells. Extension of our analysis showed that DPB3 deletion causes partial rescue of fork restart defects as well as cell cycle defects of the 14-3-3- deficient strain. However, further analysis with 2D gel electrophoresis revealed faster fork progression in dpb3∆ cells under conditions of low dNTPs, arguing that DPB3 deletion alone is sufficient to accelerate replication forks and, overall, S phase progression. Contrary to what observed with DPB3, deletion of the gene coding for the other accessory subunit of Polε, DPB4, did not affect the slow HU recovery phenotype of 14-3-3-deficient cells. Similarly, our analysis ruled out the possibility of an involvement of translesion synthesis (TLS) polymerases in the fork acceleration phenotype of dpb3∆ cells. Last conducted experiments focused on understanding the molecular mechanism by which DPB3 deletion affects the fork progression, the extent of checkpoint activation and the level of enriched ssDNA gaps upon HU treatment. Overall, our studies on physical and functional interactions between Bmh1 and an accessory subunit of Pol ε reveal a novel function for Dpb3 upon replication stress in S. cerevisiae. This study will help expanding our knowledge on pathways controlling processive DNA synthesis and its link to genomic stability.

Abstract

The integrity of DNA replication forks is important for cell viability. In replication checkpoint-deficient budding yeast, disturbances caused by DNA damaging agents possibly result in fork collapse or DNA breaks/rearrangements. Previous studies from our laboratory indicated that 14-3-3-deficient yeast cells cannot restart replication forks in response to hydroxyurea (HU) treatment. The data also indicated that in these cells ssDNA gaps accumulate behind the fork in an Exo1-dependent manner. However, while deletion of EXO1 rescued the accumulation of ssDNA gaps, it was unable to rescue HU sensitivity and the slow fork progression/restart defect of 14-3-3- deficient cells. These studies highlighted the fact that additional unknown targets of 14-3-3 proteins contribute to promote fork progression, stability and restart. From a list of established 14-3-3-interacting proteins selected in silico on the base of their involvement in DNA transactions, we attempted to identify factors that suppress fork restart upon HU-release in 14-3-3-deficient cells. We obtained evidence that Dpb3, one of the two accessory subunits of Pol ε, physically interacts with yeast 14-3-3 (Bmh1) in vivo and that deletion of DPB3 partially suppresses the HU sensitivity of 14-3-3-deficient cells. Extension of our analysis showed that DPB3 deletion causes partial rescue of fork restart defects as well as cell cycle defects of the 14-3-3- deficient strain. However, further analysis with 2D gel electrophoresis revealed faster fork progression in dpb3∆ cells under conditions of low dNTPs, arguing that DPB3 deletion alone is sufficient to accelerate replication forks and, overall, S phase progression. Contrary to what observed with DPB3, deletion of the gene coding for the other accessory subunit of Polε, DPB4, did not affect the slow HU recovery phenotype of 14-3-3-deficient cells. Similarly, our analysis ruled out the possibility of an involvement of translesion synthesis (TLS) polymerases in the fork acceleration phenotype of dpb3∆ cells. Last conducted experiments focused on understanding the molecular mechanism by which DPB3 deletion affects the fork progression, the extent of checkpoint activation and the level of enriched ssDNA gaps upon HU treatment. Overall, our studies on physical and functional interactions between Bmh1 and an accessory subunit of Pol ε reveal a novel function for Dpb3 upon replication stress in S. cerevisiae. This study will help expanding our knowledge on pathways controlling processive DNA synthesis and its link to genomic stability.

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Additional indexing

Item Type:Dissertation
Referees:Ferrari Stefano, Lopes Massimo, Cejka Petr, Schär P
Communities & Collections:04 Faculty of Medicine > Institute of Molecular Cancer Research
07 Faculty of Science > Institute of Molecular Cancer Research
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Language:English
Date:2015
Deposited On:12 Jan 2016 15:27
Last Modified:28 Jun 2016 11:21

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