The preRC protein ORCA organizes heterochromatin by assembling histone H3 lysine 9 methyltransferases on chromatin

Sumanprava Giri, Vasudha Aggarwal, Julien Pontis, Zhen Shen, Arindam Chakraborty, Abid Khan, Craig Mizzen, Kannanganattu V. Prasanth, Slimane Ait-Si-Ali, Taekjip Ha, Supriya G. Prasanth

Research output: Contribution to journalArticle


Heterochromatic domains are enriched with repressive histone marks, including histone H3lysine 9 methylation, written by lysine methyltransferases (KMTs). The pre-replication complex protein Origin Recognition Complex-Associated (ORCA/LRWD1) preferentially localizes to heterochromatic regions in post-replicated cells. Its role in heterochromatin organization remained elusive. ORCA recognizes methylated H3K9 marks and interacts with repressive KMTs, including G9a/GLP and Suv39H1 in a chromatin context-dependent manner. Single33 molecule pull-down assays demonstrate that ORCA-ORC and multiple H3K9 KMTs exist in a single complex and that ORCA stabilizes H3K9 KMT complex. Cells lacking ORCA show alterations in chromatin architecture, with significantly reduced H3K9 di- and tri-methylation at specific chromatin sites. Changes in heterochromatin structure due to loss of ORCA affects replication timing, preferentially at the late-replicating regions. We demonstrate that ORCA acts as a scaffold for the establishment of H3K9 KMT complex and its association and activity at specific chromatin sites is crucial for the organization of heterochromatin structure.

Original languageEnglish (US)
Pages (from-to)1-54
Number of pages54
Issue number4
StatePublished - Apr 29 2015
Externally publishedYes



  • Heterochromatin
  • Lysine methyl transferase
  • Single molecule pull down and replication

ASJC Scopus subject areas

  • Neuroscience(all)
  • Immunology and Microbiology(all)
  • Biochemistry, Genetics and Molecular Biology(all)

Cite this

Giri, S., Aggarwal, V., Pontis, J., Shen, Z., Chakraborty, A., Khan, A., Mizzen, C., Prasanth, K. V., Ait-Si-Ali, S., Ha, T., & Prasanth, S. G. (2015). The preRC protein ORCA organizes heterochromatin by assembling histone H3 lysine 9 methyltransferases on chromatin. eLife, 2015(4), 1-54.