Tetrahymena ORC contains a ribosomal RNA fragment that participates in rDNA origin recognition

Abstract

The Tetrahymena thermophila ribosomal DNA (rDNA) replicon contains dispersed cis-acting replication determinants, including reiterated type I elements that associate with sequence-specific, single-stranded binding factors, TIF1 through TIF4. Here, we show that TIF4, previously implicated in cell cycle-controlled DNA replication and rDNA gene amplification, is the T. thermophila origin recognition complex (TtORC). We further demonstrate that TtORC contains an integral RNA subunit that participates in rDNA origin recognition. Remarkably, this RNA, designated 26T, spans the terminal 282 nts of 26S ribosomal RNA. 26T RNA exhibits extensive complementarity to the type I element T-rich strand and binds the rDNA origin in vivo. Mutations that disrupt predicted interactions between 26T RNA and its complementary rDNA target change the in vitro binding specificity of ORC and diminish in vivo rDNA origin utilization. These findings reveal a role for ribosomal RNA in chromosome biology and define a new mechanism for targeting ORC to replication initiation sites.

Human Origin Recognition Complex Binds Preferentially to G-quadruplex-preferable RNA and Single-stranded DNA

“…The correlation between transcription and origin activation has been suggested previously (33)(34)(35)(36)(37)(38)(39), but R-loop formation in the origin region is totally unknown. On the other hand, it should be noted that Tetrahymena ORC binds to certain RNA molecules that can recruit ORC to the specific origin region (40). Thus, it should be worth investigating whether G-rich RNA/ ssDNA-binding activity of ORC would be involved in specifying the active replication origin in metazoan cells, probably by using the mutant ORC1 lacking such activity.…”

Dynamic interaction of Y RNAs with chromatin and initiation proteins during human DNA replication

“…ORC has already been shown to interact with other non-coding RNAs, which regulate initiation of DNA replication in distinct eukaryotic systems (Mohammad et al, 2007;Norseen et al, 2008;Norseen et al, 2009). Thus our data add to the concept of ORC as a target for regulation by non-coding RNAs during initiation.…”

Y RNA functions at the initiation step of mammalian chromosomal DNA replication

“…In the ciliate Tetrahymena, 26T RNA, a fragment of 26S rRNA, has been described as an integral component of the initiator complex ORC. 26T RNA is required for targeting ORC to a replication origin in the ribosomal DNA via RNA-DNA hybridisation (Mohammad et al, 2007). In human cells, a structured G-rich RNA has been shown to mediate the recruitment of ORC to the Epstein-Barr virus origin of plasmid replication (OriP) via the viral protein EBNA1 (Norseen et al, 2008).…”