Investigation into the role of the SMC5/6 complex in human cells

The Structural Maintenance of Chromosome (SMC) family of proteins are required to regulate almost all aspects of chromosome biology and are critical for genomic stability. The SMC5/6 complex, a member of this family, is composed of two SMC heterodimers and six additional Non-SMC Elements 1-6. The components of SMC5/6 possess activities including ATPases, ubiquitin and SUMO ligases. SMC5/6 is required in homologous recombination and for accurate chromosome segregation. Loss of SMC5/6 is lethal in yeasts, embryonic lethal in mice and mutations in NSMCE2 leads to primordial dwarfism and insulin resistance. This thesis focuses on a mutation in NSMCE3, found in American and Dutch families, that results in a novel chromosomal breakage syndrome characterized by fatal pulmonary disease. Another focus is the development, execution and validation of a microscopy based synthetic sick/lethal screen using cells with knockdown of NSMCE4a. Studies of SMC5/6 in yeasts predict that compromising SMC5/6 function would lead to a dependence on other DNA repair pathways. The results combined with patient data confirm that SMC5/6 is important in the absence of repair by non-homologous end joining and is particularly important under conditions of replication stress.