Originally published as Genetics Published Articles Ahead of Print on September 15, 2006.

Genetics, Vol. 174, 1801-1810, December 2006, Copyright © 2006
doi:10.1534/genetics.106.063446

Differential Requirement of DNA Replication Factors for Subtelomeric ARS Consensus Sequence Protosilencers in Saccharomyces cerevisiae

Muhammad Attiq Rehman*, Genevieve Fourel{dagger}, Amit Mathews*, Danielle Ramdin*, Maria Espinosa*, Eric Gilson{dagger} and Krassimir Yankulov*,1

* Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada and {dagger} Laboratoire de Biologie Moléculaire de la Cellule de l'Ecole Normale Supérieure de Lyon, CNRS UMR5161, IFR 128, F-69364, Lyon, France

1 Corresponding author: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.
E-mail: yankulov{at}uoguelph.ca

The establishment of silent chromatin requires passage through S-phase, but not DNA replication per se. Nevertheless, many proteins that affect silencing are bona fide DNA replication factors. It is not clear if mutations in these replication factors affect silencing directly or indirectly via deregulation of S-phase or DNA replication. Consequently, the relationship between DNA replication and silencing remains an issue of debate. Here we analyze the effect of mutations in DNA replication factors (mcm5-461, mcm5-1, orc2-1, orc5-1, cdc45-1, cdc6-1, and cdc7-1) on the silencing of a group of reporter constructs, which contain different combinations of "natural" subtelomeric elements. We show that the mcm5-461, mcm5-1, and orc2-1 mutations affect silencing through subtelomeric ARS consensus sequences (ACS), while cdc6-1 affects silencing independently of ACS. orc5-1, cdc45-1, and cdc7-1 affect silencing through ACS, but also show ACS-independent effects. We also demonstrate that isolated nontelomeric ACS do not recapitulate the same effects when inserted in the telomere. We propose a model that defines the modes of action of MCM5 and CDC6 in silencing.