Date of Award
Doctor of Philosophy
Molecular Biology, Microbiology and Biochemistry
RNAs undergo different posttranscriptional chemical modifications, which affect their structural stability and functional diversity. RNA methylation is a very common type of post-transcriptional modification and is present in all domains of life: Archaea, Eukaryotes and Bacteria. Some of these methylations are catalyzed either by a RNA-protein complex or by stand-alone enzymes. The RNA-protein complex (Ribonucleoprotein complex) is comprised of a small RNA known as the guide RNA (Box C/D RNA) and core proteins (L7Ae, Nop5, and Fibrillarin). Box C/D RNAs contain conserved regions, called box C and box D near their 5’ and 3’ termini, respectively, and their imperfect copies called box C’ and box D’, internally. A short stretch of sequence between these Boxes are known as the guide/spacer regions, as the guide region helps in recruiting and positioning a specific target RNA for modification. Both in Archaea and Eukarya, box C and box D, as well as box C’ and box D’ together can form a structure called a Kink-turn (K-turn) that is characterized by a canonical Watson-Crick base-paired stem on one side, and a non-canonical stem on the other, separated by a 3-nucleotide loop. In Archaea box C’ and D’ can also form a K-loop, where the canonical stem of K-turn is replaced by a loop. Archaeal L7Ae binds first to the K-turn or K-loop and allows the recruitment of other proteins to form the complex. The presence of a unique box C/D RNA of Haloferax volcanii, called sR-tMet has been reported previously to guide the 2’-O-methylation of C34 in elongator pre-tRNAMet. Here we tried to characterize the structure-function relationship of this guide RNA under in vivo conditions. This RNA lacks a conventional K-turn or K-loop at its C’/D’ motif. We have created an H. volcanii strain that has a genomic deletion of sR-tMet. The sR-tMet gene is not essential for H. volcanii but this sR-tMet deleted strain lacks the 2’-O-methylation of C34 of its elongator tRNAMet. Unlike the close sR-tMet homologs (sR8 from Methanocaldococcus jannaschii and sR49 from Pyrococcus abyssi), the Box C’/D’ motif of sR-tMet is neither a K-turn nor a K-loop. The introduction of proper K-loop in the Box C’/D’ motif (sR-tMet with K-loop) abolished its Cm34 modification function in ΔsR-tMet strain. Direct interaction between L7Ae and the K-loop is not an absolute requirement for its function. However, disruption of the G/A and A/G pairing in Box C/D motif and Box D’ suggests the importance of these non-Watson crick base pairings in respect to sR-tMet’s function. Several other mutational studies have revealed that peculiar sR-tMet guide RNA from H. volcanii, behaves more like a Eukaryotic Box C/D RNA (where the K-loop is not required and presence of longer spacer length) than regular Archaeal one. Pseudouridine synthase 10 (Pus10) is the most recently identified Ψ synthase, found only in higher eukaryotes and Archaea. Archaeal Pus10 produces either tRNA Ψ55 or both tRNA Ψ54 and Ψ55 modifications. In Human, its Ψ synthase activity is not yet confirmed and interestingly it has been implicated in apoptosis. Herein for the first time we revealed that this putative RNA Ψ synthase protein, Human Pus10 (HuP10), translocates from the nucleus to the cytoplasm in TRAIL induced apoptosis. This nucleo-cytoplasmic movement of HuP10 occurs through the CRM1 mediated nuclear export pathway and Caspase 3 influences this movement. HuP10 also mediates crosstalk between the extrinsic and intrinsic pathways during TRAIL-induced apoptosis. Other than its involvement in apoptosis, we have also uncovered that HuP10 is involved in regulation of cell proliferation. Depletion (knockdown) of this protein in different cancer cell lines, promotes cell migration and anchorage-independent cell growth in the absence of any apoptotic stimulation.
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