Science · 1993 · 316 citations · 42 references
Life SciencesGeneticsMolecular BiologyDna ReplicationGene ExpressionTranscriptional RegulationGene SilencingReplication In EukaryotesReplication OriginsSilencer ElementsTranscriptional Regulation In EukaryotesTranscriptional SilencingDna Recognition SequencesEssential Gene IdentificationOrigin Recognition ComplexOrigin Recognition SequencesReplication Origin Firing RegulationReplication Origin RecognitionSilencer Binding SitesTemperature-sensitive Mutants
In Saccharomyces cerevisiae, the HMR-E silencer blocks site-specific interactions between proteins and their recognition sequences in the vicinity of the silencer. Silencer function is correlated with the firing of an origin of replication at HMR-E. An essential gene with a role in transcriptional silencing was identified by means of a screen for mutations affecting expression of HMR. This gene, known as ORC2, was shown to encode a component of the origin recognition complex that binds yeast origins of replication. A temperature-sensitive mutation in ORC2 disrupted silencing in cells grown at the permissive temperature. At the restrictive temperature, the orc2-1 mutation caused cell cycle arrest at a point in the cell cycle indicative of blocks in DNA replication. The orc2-1 mutation also resulted in the enhanced mitotic loss of a plasmid, suggestive of a defect in replication. These results provide strong evidence for an in vivo role of ORC in both chromosomal replication and silencing, and provide a link between the mechanism of silencing and DNA replication.
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