title: Directional telomeric silencing and lack of canonical B1 elements in two silencer Autonomously Replicating Sequences in S. cerevisiae.
abstract: BACKGROUND
  Autonomously Replicating Sequences (ARS) in S. cerevisiae serve as origins of DNA replication or as components of cis-acting silencers, which impose positional repression at the mating type loci and at the telomeres. Both types of ARS can act as replicators or silencers, however it is not clear how these quite diverse functions are executed. It is believed that all ARS contain a core module of an essential ARS Consensus Sequence (ACS) and a non-essential B1 element.
  
  
  RESULTS
  We have tested how the B1 elements contribute to the silencer and replicator function of ARS. We report that the ACS-B1 orientation of ARS has a profound effect on the levels of gene silencing at telomeres. We also report that the destruction of the canonical B1 elements in two silencer ARS (ARS317 and ARS319) has no effect on their silencer and replicator activity.
  
  
  CONCLUSIONS
  The observed orientation effects on gene silencing suggest that ARSs can act as both proto-silencers and as insulator elements. In addition, the lack of B1 suggests that the ACS-B1 module could be different in silencer and replicator ARS.
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada.
authors.forename: Patricia
authors.initials: P
authors.lastname: Chisamore-Robert
authors.forename: Samantha
authors.initials: S
authors.lastname: Peeters
authors.forename: Kristina
authors.initials: K
authors.lastname: Shostak
authors.forename: Krassimir
authors.initials: K
authors.lastname: Yankulov
mesh_terms: D001483:Base Sequence; D015825:Chromosomes, Fungal / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication; D020868:Gene Silencing; D005800:Genes, Fungal; D009154:Mutation; D018741:Replication Origin; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D016615:Telomere / Q000235:genetics / Q000378:metabolism*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; C554167:URA3 protein, S cerevisiae