T rypanosoma brucei Orc 1 is essential for nuclear DNA replication and affects both VSG silencing and VSG switching

• Published in: Molecular microbiology Vol. 87; no. 1; pp. 196 - 210
• Main Authors: Benmerzouga, Imaan, Concepción‐Acevedo, Jeniffer, Kim, Hee‐Sook, Vandoros, Anthula V., Cross, George A. M., Klingbeil, Michele M., Li, Bibo
• Format: Journal Article
• Language: English
• Published: 01.01.2013
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.12093

Summary Binding of the O rigin R ecognition C omplex ( ORC ) to replication origins is essential for initiation of DNA replication, but ORC has non‐essential functions outside of DNA replication, including in heterochromatic gene silencing and telomere maintenance. T rypanosoma brucei, a protozoan parasite that causes human A frican trypanosomiasis, uses antigenic variation as a major virulence mechanism to evade the host's immune attack by expressing its major surface antigen, the V ariant S urface G lycoprotein ( VSG ), in a monoallelic manner. An Orc 1/ Cdc 6 homologue has been identified in T . brucei, but its role in DNA replication has not been directly confirmed and its potential involvement in VSG repression or switching has not been thoroughly investigated. In this study, we show that TbOrc 1 is essential for nuclear DNA replication in mammalian‐infectious bloodstream and tsetse procyclic forms ( BF and PF ). Depletion of TbOrc 1 resulted in derepression of telomere‐linked silent VSG s in both BF and PF , and increased VSG switching particularly through the in situ transcriptional switching mechanism. TbOrc 1 associates with telomere repeats but appears to do so independently of two known T . brucei telomere proteins, TbRAP 1 and TbTRF . We conclude that TbOrc 1 has conserved functions in DNA replication and is also required to control telomere‐linked VSG expression and VSG switching.