Type I elements mediate replication fork pausing at conserved upstream sites in the Tetrahymena thermophila ribosomal DNA minichromosome.

Journal Article (Journal Article)

Two-dimensional gel electrophoresis was used to study replication of the Tetrahymena thermophila ribosomal DNA (rDNA) minichromosome. During vegetative growth, the rDNA is replicated exclusively from origins in the 5' nontranscribed spacer (NTS). Whereas replication fork movement through the rest of the chromosome appears to be continuous, movement through the 5' NTS is not. Replication forks arrest transiently at three prominent replication fork pausing sites (RFPs) located in or immediately adjacent to nucleosome-free regions of the 5' NTS. Pausing at these sites is dramatically diminished during replication in Escherichia coli, suggesting that chromatin organization or Tetrahymena-specific proteins may be required. A conserved tripartite sequence was identified at each pausing site. Mutations in type I elements diminish pausing at proximal RFPs. Hence, type I elements, previously shown to control replication initiation, also regulate elongation of existing replication forks. Studies with rDNA transformants revealed a strong directional bias for fork pausing. Strong pausing only occurred in forks moving toward the rRNA-coding region. We propose that fork pausing in the 5' NTS evolved to synchronize replication and transcription of the downstream rRNA genes.

Full Text

Duke Authors

Cited Authors

  • MacAlpine, DM; Zhang, Z; Kapler, GM

Published Date

  • August 1997

Published In

Volume / Issue

  • 17 / 8

Start / End Page

  • 4517 - 4525

PubMed ID

  • 9234709

Pubmed Central ID

  • PMC232305

International Standard Serial Number (ISSN)

  • 0270-7306

Digital Object Identifier (DOI)

  • 10.1128/MCB.17.8.4517


  • eng

Conference Location

  • United States