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DTSTAMP:20260405T211124Z
UID:1592229600@ist.ac.at
DTSTART:20200615T160000
DTEND:20200615T170000
DESCRIPTION:Speaker: Kim Nasmyth\nhosted by Thomas Henzinger\nAbstract: Thi
 s Institute Colloquium is offered as a webinar.  If you would like to att
 end this webinar\, please register here (https://istaustria.microsoftcrmp
 ortals.com/event/registration?id=20200615_Institute_Colloquium_Kim_Nasmyth
 317980169).In addition to extruding long loops of DNA\, cohesin topologica
 lly entraps within its SMC-kleisin ring (S-K) individual DNAs during G1 an
 d sister DNAs during S-phase. Co-entrapment of sister DNAs is thought to b
 e the mechanism by which cohesin holds sister chromatids together\, a proc
 ess crucial for mitotic and meiotic chromosome segregation.  All three co
 hesin activities require two related hook-shaped proteins called Scc2 and 
 Scc3. Using a combination of cysteine pair substitutions and thiol-specifi
 c crosslinking we provide a rigorous demonstration of entrapment activity 
 in vitro. We show that Scc2 alone promotes entrapment of DNAs in the E-S a
 nd E-K compartments between ATP-bound engaged heads and the SMC hinge and 
 associated kleisin respectively. This process does not require ATP hydroly
 sis nor is it accompanied by entrapment within S-K rings\, which is a slow
 er process that requires addition of Scc3 and is stimulated by ATP hydroly
 sis. Though cohesin can load onto chromosomes throughout the cell cycle\, 
 it normally only builds cohesion during S phase. A key question is whether
  cohesion is generated by conversion of cohesin complexes associated with 
 un-replicated DNAs ahead of replication forks into cohesive structures beh
 ind them\, or from nucleoplasmic cohesin that is loaded de novo onto nasce
 nt DNAs associated with forks\, a process that would be dependent on cohes
 in’s Scc2 subunit. We show here that in S. cerevisiae\, both mechanisms 
 exist and that each requires a different set of non-essential replisome-as
 sociated proteins. Cohesion produced by cohesin conversion requires Tof1/C
 sm3\, Ctf4 and Chl1 (TCCC) but not Scc2 while that created by Scc2-depende
 nt de novo loading at replication forks requires the Ctf18-RFC complex. Th
 ough inactivation of either pathway individually merely reduces the effici
 ency of cohesion establishment\, simultaneous inactivation resembles the e
 ffect of cohesin ablation and is lethal. The association of specific repli
 some proteins with different types of cohesion establishment opens the way
  to a mechanistic understanding of an aspect of DNA replication unique to 
 eukaryotic cells.
LOCATION:Webinar\, ISTA
ORGANIZER:arinya.eller@ist.ac.at
SUMMARY:Kim Nasmyth: [Webinar] The establishment of sister chromatid cohesi
 on is an aspect of the replisome unique to eukaryotic cells
URL:https://talks-calendar.ista.ac.at/events/2783
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