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Fai Y. Siu
SRP is a ribonucleoprotein complex that selectively transports ribosome
nascent-chain complex (RNC) to the endoplasmic reticulum of eukaryotes
or the inner membrane of bacteria. The selectivity is mainly defined
by the level of hydrophobicity of the signal sequence peptide that is on
the nascent chain. Upon binding to the signal sequence, the eukaryotic
SRP causes translational arrest, interacts with the SRP receptor (SR)
in a GTP- dependent manner, and the RNC is delivered to the translocon
upon GTP hydrolysis.
Part I of my thesis project is to determine the effect of mutation in
the tetraloop of the RNA in the E coli SRP system. It has been
demonstrated by Jagath et al that mutating the tetraloop of
4.5S RNA from GGAA to UUCG leads to a loss of the SRP and receptor (ftsY)
complex formation by gel retardation assay. By revealing the mechanism of
the mutant 4.5S RNA in the disruption SRP and ftsY complex formation, we
can get a better understanding of the role the RNA has in the SRP system.
The second part of my thesis project is to obtain the X-ray structure
of the human Dicer with and without a RNA substrate. Dicer is an
RNaseIII enzyme in the RNAi pathway that cleaves long double stranded
RNA into short interfering RNA (siRNA) that are approximately 21nt long.
The siRNA is loaded into the RISC complex and guides this complex to
its target mRNA by sequence complementation. After targeting, the RISC
complex cleaves the mRNA, and thus, the mRNA is no longer translated.
The structure of the human Dicer will determine the cleave mechanism of
this multi-domain enzyme and may also give clues to better design RNA
substrates for gene silencing through the RNAi pathway.
Selected Publications
Siu, F.Y., Spanggord, R.J. and Doudna, J.A. (2006)
SRP RNA provides the physiologically essential GTPase activation function in
cotranslational protein targeting.
RNA 13, 240-250.
(1.1MB .pdf)
Spanggord, R.J., Siu, F., Ke, A. and Doudna, J.A. (2005)
RNA-mediated interaction between the peptide-binding and GTPase domains of the signal recognition particle.
Nat. Struct. Mol. Biol. 12, 1116-1122.
(484KB .pdf)
(Figures)
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