Biomedical subjects

Kangseok Lee

Publications and source records attributed to Kangseok Lee.

8 recordsLinked to original sources

PubMed2006

Differential modulation of E. coli mRNA abundance by inhibitory proteins that alter the composition of the degradosome.

In Escherichia coli the initial step in the processing or decay of many messenger and structural RNAs is mediated by the endonuclease RNase E, which forms the core of a large RNA-catalysis machine termed the degradosome. Previous experiments have identified a protein that globally modulates RNA abundance by binding to RNase E and regulating its endonucleolytic activity. Here we report the discovery of RraB, which interacts with a different site on RNase E and interferes with cleavage of a different set of transcripts. We show that expression of RraA or RraB in vivo is accompanied by dramatic, distinct, and inhibitor-specific changes in degradosome composition--and that these are in turn associated with alterations in RNA decay and global transcript abundance profiles that are dissimilar to the profile observed during simple RNase E deficiency. Our results reveal the existence of endonuclease binding proteins that modulate the remodelling of degradosome composition in bacteria and argue that such degradosome remodelling is a mechanism for the differential regulation of RNA cleavages in E. coli.

Endoribonucleases↗

PubMed2006

RraA rescues Escherichia coli cells over-producing RNase E from growth arrest by modulating the ribonucleolytic activity.

RraA is an evolutionary conserved protein inhibitor of RNase E, which catalyzes the initial step in the decay and processing of numerous RNAs in Escherichia coli and forms the core component of the degradosome, a large protein complex involved in RNA metabolism. Here, we report that co-expression of RraA reduces the ribonucleolytic activity in cells over-producing RNase E and consequently rescues these cells from growth arrest. These findings suggest that inability of cells over-producing RNase E to normally grow results from increased cellular ribonucleolytic activity and RraA is able to effectively modulate the catalytic activity of RNase E in vivo.

Catalysis↗

PubMed2006

RNase E maintenance of proper FtsZ/FtsA ratio required for nonfilamentous growth of Escherichia coli cells but not for colony-forming ability.

Inactivation or deletion of the RNase E-encoding rne gene of Escherichia coli results in the growth of bacterial cells as filamentous chains in liquid culture (K. Goldblum and D. Apirion, J. Bacteriol. 146:128-132, 1981) and the loss of colony-forming ability (CFA) on solid media. RNase E dysfunction is also associated with abnormal processing of ftsQAZ transcripts (K. Cam, G. Rome, H. M. Krisch, and J.-P. Bouché, Nucleic Acids Res. 24:3065-3070, 1996), which encode proteins having a central role in septum formation during cell division. We show here that RNase E regulates the relative abundances of FtsZ and FtsA proteins and that RNase E depletion results in decreased FtsZ, increased FtsA, and consequently an altered FtsZ/FtsA ratio. However, while restoration of the level of FtsZ to normal in rne null mutant bacteria reverses the filamentation phenotype, it does not restore CFA. Conversely, overexpression of a related RNase, RNase G, in rne-deleted bacteria restores CFA, as previously reported, without affecting FtsZ abundance. Our results demonstrate that RNase E activity is required to maintain a proper cellular ratio of the FtsZ and FtsA proteins in E. coli but that FtsZ deficiency does not account for the nonviability of cells lacking RNase E.

Culture Media↗

PubMed2005

Transcriptional factor FOXL2 interacts with DP103 and induces apoptosis.

Blepharophimosis-ptosis-epicanthus inversus syndrome type I is an autosomal disorder caused by mutations in FOXL2 gene and associated with premature ovarian failure in women by a dominant inheritance. FOXL2 is a recently identified protein that belongs to forkhead family transcription factor, of which signaling pathways are still unknown. Here, we show that FOXL2 induces apoptosis in both Chinese hamster ovary cells and rat granulosa cells, and it interacts with DP103, a DEAD box-containing protein. Overexpression of DP103 itself did not affect cell viability while its coexpression with FOXL2 led to the potentiation of cell death. Our results present previously undiscovered functions of these proteins, an apoptotic activity of FOXL2 in the ovary and a modulating activity of DP103 by interacting with FOXL2.

Animals↗

PubMed2004

Dispersion polymerization of methyl methacrylate with a novel bifunctional polyurethane macromonomer as a reactive stabilizer.

A novel macromonomer of vinyl-terminated bifunctional polyurethane was synthesized and applied to the dispersion polymerization of MMA in ethanol. The existence of the vinyl terminal groups and the grafted macromonomer with PMMA was verified using 1H NMR and 13C NMR. The stable and monodisperse PMMA microspheres having a weight-average diameter of 5.09 microm and a good uniformity of 1.01 were obtained with 20 wt% polyurethane macromonomer. The molecular weight increased, but the size of the synthesized PMMA microspheres decreased with the macromonomer concentration since the macromonomer acts as a reactive stabilizer in dispersion polymerization. Furthermore, the molecular weight of the PMMA prepared by the use of the macromonomer was approximately twofold higher than that prepared by a conventional stabilizer, poly(N-vinylpyrrolidone). The higher molecular weight is thought to originate from the grafting and a possibly slight crosslinking of PMMA molecules due to the bifunctional reactive groups at the ends of macromonomer chains.

Magnetic Resonance Spectroscopy↗

PubMed2003

RraA. a protein inhibitor of RNase E activity that globally modulates RNA abundance in E. coli.

Ribonuclease E (RNase E) has a key role in mRNA degradation and the processing of catalytic and structural RNAs in E. coli. We report the discovery of an evolutionarily conserved 17.4 kDa protein, here named RraA (regulator of ribonuclease activity A) that binds to RNase E and inhibits RNase E endonucleolytic cleavages without altering cleavage site specificity or interacting detectably with substrate RNAs. Overexpression of RraA circumvents the effects of an autoregulatory mechanism that normally maintains the RNase E cellular level within a narrow range, resulting in the genome-wide accumulation of RNase E-targeted transcripts. While not required for RraA action, the C-terminal RNase E region that serves as a scaffold for formation of a multiprotein degradosome complex modulates the inhibition of RNase E catalytic activity by RraA. Our results reveal a possible mechanism for the dynamic regulation of RNA decay and processing by inhibitory RNase binding proteins.

Blotting, Western↗

PubMed2003

A Streptomyces coelicolor functional orthologue of Escherichia coli RNase E shows shuffling of catalytic and PNPase-binding domains.

Previous work has detected an RNase E-like endoribonucleolytic activity in cell extracts obtained from Streptomyces. Here, we identify a Streptomyces coelicolor gene, rns, encoding a 140 kDa protein (RNase ES) that shows endoribonucleolytic cleavage specificity characteristic of RNase E, confers viability on and allows propagation of Escherichia coli cells lacking RNase E and accomplishes RNase E-like regulation of plasmid copy number in E. coli. However, notwithstanding its complementation of rne-deleted E. coli, RNase ES did not accurately process 9S rRNA from E. coli. Additionally, whereas RNase E is normally required for E. coli survival, rns is not an essential gene in S. coelicolor. Deletion analysis mapped the catalytic domain of RNase ES near its centre and showed that regions located near the RNase ES termini interact with an S. coelicolor homologue of polynucleotide phosphorylase (PNPase) - a major component of E. coli RNase E-based degradosomes. The interacting arginine- and proline-rich segments resemble the C-terminally located degradosome scaffold region of E. coli RNase E. Our results indicate that RNase ES is a structurally shuffled RNase E homologue showing evolutionary conservation of functional RNase E-like enzymatic activity, and suggest the existence of degradosome-like complexes in Gram-positive bacteria.

Bacterial Proteins↗

PubMed2002

RNase G complementation of rne null mutation identifies functional interrelationships with RNase E in Escherichia coli.

The Escherichia coli endoribonucleases RNase E (Rne) and RNase G (Rng) have sequence similarity and broadly similar sequence specificity. Whereas the absence of Rne normally is lethal, we show here that E. coli bacteria that lack the rne gene can be made viable by overexpression of Rng. Rng-complemented cells accumulated precursors of 5S ribosomal RNA (rRNA) and the RNA component of RNase P (i.e. M1 RNA), indicating that normal processing of these Rne-cleaved RNAs was not restored by RNase G; additionally, neither 5S rRNA nor M1 RNA was generated from precursors by RNase G cleavage in vitro. Using DNA microarrays containing 4405 Escherichia coli open reading frames (ORFs), we identified mRNAs whose steady-state level was affected by Rne, Rng or the N-terminal catalytic domain of RNase E. Most transcript species affected by RNase E deficiency were also elevated in an rne deletion mutant complemented by Rng. However, approximately 100 mRNAs that accumulated in Rne-deficient cells were decreased by rng-complemention, thus identifying targets whose processing or degradation may be the basis for RNase E essentiality. Remarkably prominent in this group were mRNAs implicated in energy-generating pathways or in the synthesis or degradation of macromolecules.

Base Sequence↗