Impaired replication elongation in Tetrahymena mutants deficient in histone H3 Lys 27 monomethylation

Genes Dev. 2013 Aug 1;27(15):1662-79. doi: 10.1101/gad.218966.113. Epub 2013 Jul 24.


Replication of nuclear DNA occurs in the context of chromatin and is influenced by histone modifications. In the ciliate Tetrahymena thermophila, we identified TXR1, encoding a histone methyltransferase. TXR1 deletion resulted in severe DNA replication stress, manifested by the accumulation of ssDNA, production of aberrant replication intermediates, and activation of robust DNA damage responses. Paired-end Illumina sequencing of ssDNA revealed intergenic regions, including replication origins, as hot spots for replication stress in ΔTXR1 cells. ΔTXR1 cells showed a deficiency in histone H3 Lys 27 monomethylation (H3K27me1), while ΔEZL2 cells, deleting a Drosophila E(z) homolog, were deficient in H3K27 di- and trimethylation, with no detectable replication stress. A point mutation in histone H3 at Lys 27 (H3 K27Q) mirrored the phenotype of ΔTXR1, corroborating H3K27me1 as a key player in DNA replication. Additionally, we demonstrated interactions between TXR1 and proliferating cell nuclear antigen (PCNA). These findings support a conserved pathway through which H3K27me1 facilitates replication elongation.

Keywords: H3 Lys 27 methylation; histone methyltransferase; replication elongation; replication origin; replication stress; ssDNA.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • DNA Replication / genetics*
  • DNA, Single-Stranded / metabolism
  • Histones / genetics
  • Histones / metabolism*
  • Methylation
  • Mutation
  • Proliferating Cell Nuclear Antigen / metabolism
  • Repressor Proteins / metabolism
  • Tetrahymena thermophila / genetics*
  • Tetrahymena thermophila / metabolism*


  • DNA, Single-Stranded
  • Histones
  • Proliferating Cell Nuclear Antigen
  • Repressor Proteins