Reference: Bairwa NK, et al. (2010) Replication fork arrest and rDNA silencing are two independent and separable functions of the replication terminator protein Fob1 of Saccharomyces cerevisiae. J Biol Chem 285(17):12612-9

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Abstract


The replication terminator protein Fob1 of Saccharomyces cerevisiae (Sc Fob1) is multifunctional and it not only promotes polar replication fork arrest at the tandem Ter sites located in the intergenic spacer region (IGS) of rDNA but also loads the NAD-dependent histone deacetylase, Sir2, at the Ter sites via a protein complex called RENT (Regulator of Nucleolar Silencing and Telophase exit). Sir2 is a component of the RENT complex and its loading not only silences intra-chromatid recombination in rDNA but also RNA polymerase II-catalyzed transcription. Here, we present three lines of evidence showing that the two aforementioned activities of Fob1 are independent of each other and functionally separable. First, a Fob1 ortholog of S. baynus (Sb Fob1) expressed in a fob1 deleted strain of S. cerevisiae restored polar fork arrest at Ter but not rDNA silencing. Second, a mutant form (I407T) of Sc Fob1 retained normal fork arresting activity but was severely defective in rDNA silencing. We show further that the silencing defect of Sb Fob1 and the I407T mutant of Sc Fob1 were caused by the failure of the proteins to interact with two members of the Sc RENT complex namely Sc Sir2 and Sc Net1. Third, deletions of the intra-S phase checkpoint proteins Tof1 and Csm3 abolished fork arrest by Fob1 at Ter without causing loss of silencing. Taken together, the data support the conclusion that unlike some other functions of Fob1, rDNA silencing at Ter is independent of fork arrest.

Reference Type
Journal Article
Authors
Bairwa NK, Zzaman S, Mohanty BK, Bastia D
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