The Ctf18 RFC-like complex positions yeast telomeres but does not specify their replication time

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Telomeres, the chromosome ends, are typically clustered at the nuclear periphery in Saccharomyces cerevisiae.
• Peripheral nuclear positioning of chromatin correlates with late DNA replication in both yeast and mammalian cells.

Purpose of the Study:

• To investigate the role of the Ctf18, Ctf8, and Dcc1 complex in telomere positioning.
• To determine the relationship between telomere positioning, DNA replication timing, and the Ku and Sir pathways.

Main Methods:

• Genetic analysis of Saccharomyces cerevisiae mutants lacking Ctf18.
• Observation of telomere localization and DNA replication timing.
• Assessment of Ku and Sir complex function in telomere positioning.

Main Results:

• The Ctf18 RFC-like complex is essential for the perinuclear positioning of telomeres.
• Mislocalized telomeres in ctf18 mutants still replicate late, decoupling positioning from replication timing.
• Ctf18 is required for the full function of both Ku and Sir pathways in telomere positioning.
• Ctf18 is not required for the tethering of non-telomeric loci.

Conclusions:

• The Ctf18 RFC-like complex plays a vital role in telomere localization to the nuclear periphery.
• This complex modifies telomeric chromatin, making it competent for peripheral localization.
• Telomere positioning is regulated by mechanisms distinct from, but interacting with, DNA replication timing and chromatin modification.