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TTHERM_00865050 is a homolog of annotated and functionally characterized Orc1 in other experimental organisms (24% amino acid sequence identity, 49% similarity to human Orc1). Orc1 is a component of the heterohexameric origin recognition complex (ORC) found to be involved in initiation of DNA replication. TtOrc1 has canonical Walker A and B motifs (involved in ATP binding and hydrolysis). TtORC is unusual in that it contains an integral RNA subunit (26T RNA) that binds to its cognate DNA target in the ribosomal DNA (rDNA) replication origin.
Nucleic Acid Interactions (with the ORC complex):
26T RNA (5’-AUGUCUAAGUGUGAUGAUAAACGAAAAAAAAUAAAAAUUAA-3’).
Type I element T-rich strand: essential cis-acting replication determinant in ribosomal DNA origin of replication. (Location 5’ non-transcribed spacer)
(C3 rDNA type IB element T-rich strand, T51: 5’-CTCAAAAGTTGCAAAAGTTCGGAAGGTTTACTATTTTTGTTTTTTTTTT-3’). – requires 26T RNA and ATP
dsDNA – non rDNA chromosomes
Regulation & Expression:
mRNA and protein: Cell cycle regulated
Maximal protein expression at G1/S border, degraded in S phase
Ref:19153611: Donti TR, Datta S, Sandoval PY, Kapler GM (2009) Differential targeting of Tetrahymena ORC to ribosomal DNA and non-rDNA replication origins. The EMBO journal 28(3):223-33
Ref:18007594: Mohammad MM, Donti TR, Sebastian Yakisich J, Smith AG, Kapler GM (2007) Tetrahymena ORC contains a ribosomal RNA fragment that participates in rDNA origin recognition. The EMBO journal 26(24):5048-60
Ref:12832485: Mohammad M, York RD, Hommel J, Kapler GM (2003) Characterization of a novel origin recognition complex-like complex: implications for DNA recognition, cell cycle control, and locus-specific gene amplification. Molecular and cellular biology 23(14):5005-17
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