Interplay between Top1 and Mms21/Nse2 mediated sumoylation in stable maintenance of long chromosomes

Abstract

Genetic information in cells is encrypted in DNA molecules forming chromosomes of varying sizes. Accurate replication and partitioning of chromosomes in the crowded cellular milieu is a complex process involving duplication, folding and movement. Longer chromosomes may be more susceptible to mis-segregation or DNA damage and there may exist specialized physiological mechanisms preventing this. Here, we present genetic evidence for such a mechanism which depends on Mms21/Nse2 mediated sumoylation and topoisomerase-1 (Top1) for maintaining stability of longer chromosomes. While mutations inactivating Top1 or the SUMO ligase activity of Mms21 (mms21sl) individually destabilized yeast artificial chromosomes (YACs) to a modest extent, the mms21sl top1 double mutant exhibited a synthetic-sick phenotype, and showed preferential destabilization of the longer chromosome relative to shorter chromosomes. In contrast, an smc6-56 top1 mutant defective in Smc6, another subunit of the Smc5/6 complex, of which Mms21 is a component, did not show such a preferential enhancement in frequency of loss of the longer YAC, indicating that this defect may be specific to the deficiency in SUMO ligase activity of Mms21 in the mms21sl top1 mutants. In addition, mms21sl top1 double mutants harboring a longer fusion derivative of natural yeast chromosomes IV and XII displayed reduced viability, consistent with enhanced chromosome instability, relative to single mutants or the double mutant having the natural (shorter) non-fused chromosomes. Our findings reveal a functional interplay between Mms21 and Top1 in maintenance of longer chromosomes, and suggest that lack of sumoylation of Mms21 targets coupled with Top1 deficiency is a crucial requirement for accurate inheritance of longer chromosomes.

The Main Role of Srs2 in DNA Repair Depends on Its Helicase Activity, Rather than on Its Interactions with PCNA or Rad51

“…The yeast Saccharomyces cerevisiae is an excellent model to isolate and study mutants that shed light on the processes that maintain genome stability ( 2 , 3 ). The Srs2 helicase has a major role in HR regulation; it is generally thought that its role is to suppress HR events at an early stage by dismantling the Rad51-presynaptic filament ( 4 , 5 ).…”

DNA Topoisomerase II modulates acetyl-regulation of cohesin-mediated chromosome dynamics

“…However, data in S. cerevisiae functionally link both Top1 (Mahendrawada, et al 2016) and Top2 (Kanno, et al 2015) to the Smc5/6 complex. While the precise defects conferred by the mutant alleles used may differ between systems, these findings are provocative and suggest the functional axis may be a more general feature of mitotic progression that is not limited to the prophase pathway, which does not control cohesin dynamics in S. cerevisiae .…”

Emerging Roles for Human MMS21, NSMCE2, in Development and Disease

“…While its function remains elusive, there is clear evidence of its involvement in multiple chromosomal processes. The Smc5/6 complex plays an important role in mitotic proliferation as well as meiosis, and in maintenance of chromosome stability [10][11][12]. It is involved in rescue of collapsed replication forks [13,14], progression of replication forks [15,16] DNA double strand break repair and resolution of recombination intermediates [17,18].…”

“…While its roles in chromosome stability are well appreciated and arise from its ability to modify numerous chromosomal proteins involved in chromosome organization, segregation and repair [9,10,12], new roles in nuclear-cytoplasmic transport and metabolism are being identified. Mms21 in budding yeast, sumoylates the nuclear import receptor Kap114, that is required for import of transcription factors and other cargos across the nuclear pore [32].…”