Bustard DE, Menolfi D, Jeppsson K, Ball LG, Dewey SC, Shirahige K, Sjogren C, Branzei D, Cobb JA

The Smc5/6 complex belongs to the Structural Maintenance of Chromosomes (SMC) family that also includes cohesin and condensin. In Saccharomyces cerevisiae the Smc5/6 complex contains six essential Non-Smc-Elements (Nse1-6). Very little is known about how these additional elements contribute to complex function except for Nse2/Mms21, which is an E3 SUMO ...

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ligase important for Smc5 sumoylation. Characterization of two temperature sensitive mutants, nse5-ts1 and nse5-ts2, demonstrates the importance of Nse5 within the Smc5/6 complex for its stability and functionality at forks during hydroxyurea (HU)-induced replication stress. Both NSE5 alleles showed a marked reduction in Smc5 sumoylation to levels lower than those observed with mms21-11, a mutant of Mms21 that is deficient in SUMO ligase activity. However, a phenotypic comparison of nse5-ts1 and nse5-ts2 revealed a separation of importance between Smc5 sumoylation and the function of the Smc5/6 complex during replication. Only cells carrying the nse5-ts1 allele exhibited defects such as dissociation of the replisome from stalled forks, the formation of fork-associated homologous recombination (HR) intermediates, and HU sensitivity that is additive with mms21-11. These defects are attributed to a failure in Smc5/6 localization to forks in nse5-ts1 cells. Overall, these data support the premise that Nse5 is important for vital interactions between components within the Smc5/6 complex, which is a prerequisite for its functionality during replication stress.

Date: Feb. 02, 2012

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