Biomedical subjects

Hye-Jung Chung

Publications and source records attributed to Hye-Jung Chung.

5 recordsLinked to original sources

PubMed2006

The FUSE/FBP/FIR/TFIIH system is a molecular machine programming a pulse of c-myc expression.

FarUpStream Element (FUSE) Binding Protein (FBP) binds the human c-myc FUSE in vitro only in single-stranded or supercoiled DNA. Because transcriptionally generated torsion melts FUSE in vitro even in linear DNA, and FBP/FBP Interacting Repressor (FIR) regulates transcription through TFIIH, these components have been speculated to be the mechanosensor (FUSE) and effectors (FBP/FIR) of a real-time mechanism controlling c-myc transcription. To ascertain whether the FUSE/FBP/FIR system operates according to this hypothesis in vivo, the flux of activators, repressors and chromatin remodeling complexes on the c-myc promoter was monitored throughout the serum-induced pulse of transcription. After transcription was switched on by conventional factors and chromatin regulators, FBP and FIR were recruited and established a dynamically remodeled loop with TFIIH at the P2 promoter. In XPB cells carrying mutant TFIIH, loop formation failed and the serum response was abnormal; RNAi depletion of FIR similarly disabled c-myc regulation. Engineering FUSE into episomal vectors predictably re-programmed metallothionein-promoter-driven reporter expression. The in vitro recruitment of FBP and FIR to dynamically stressed c-myc DNA paralleled the in vivo process.

Cell Line↗

PubMed2006

FBPs are calibrated molecular tools to adjust gene expression.

The three far-upstream element (FUSE) binding protein (FBP) family members have been ascribed different functions in gene regulation. They were therefore examined with various biochemical, molecular biological, and cell biological tests to evaluate whether their sequence differences reflect functional customization or neutral changes at unselected residues. Each FBP displayed a characteristic profile of intrinsic transcription activation and repression, binding with protein partners, and subcellular trafficking. Although some differences, such as weakened FBP3 nuclear localization, were predictable from primary sequence differences, the unexpected failure of FBP3 to bind the FBP-interacting repressor (FIR) was traced to seemingly conservative substitutions within a small patch of an N-terminal alpha-helix. The transactivation strength and the FIR-binding strength of the FBPs were in the opposite order. Despite their distinguishing features and differential activities, the FBPs traffic to shared subnuclear sites and regulate many common target genes, including c-myc. Though a variety of functions have been attributed to the FBPs, based upon their panel of shared and unique features, we propose that they constitute a molecular regulatory kit that tunes the expression of shared targets through a common mechanism.

Amino Acid Sequence↗

PubMed2005

c-myc expression: keep the noise down!

The c-myc proto-oncogene encodes a nuclear protein that is deregulated and/or mutated in most human cancers. Acting primarily as an activator and sometimes as a repressor, MYC protein controls the synthesis of up to 10-15% of genes. The key MYC targets contributing to oncogenesis are incompletely enumerated and it is not known whether pathology arises from the expression of physiologic targets at abnormal levels or from the pathologic response of new target genes that are not normally regulated by MYC. Regardless of which, available evidence indicates that the level of MYC expression is an important determinant of MYC biology. The c-myc promoter has architectural and functional features that contribute to uniform expression and help to prevent or mitigate conditions that might otherwise create noisy expression. Those features include the use of an expanded proximal promoter, the averaging of input from dozens of transcription factors, and real-time feedback using the supercoil-deformable Far UpStream Element (FUSE) as physical sensor of ongoing transcriptional activity, and the FUSE binding protein (FBP) as well as the FBP interacting repressor (FIR) as effectors to enforce normal transcription from the c-myc promoter.

Animals↗

PubMed2004

The dynamic response of upstream DNA to transcription-generated torsional stress.

The torsional stress caused by counter-rotation of the transcription machinery and template generates supercoils in a closed topological domain, but has been presumed to be too short-lived to be significant in an open domain. This report shows that transcribing RNA polymerases dynamically sustain sufficient torsion to perturb DNA structure even on linear templates. Assays to capture and measure transcriptionally generated torque and to trap short-lived perturbations in DNA structure and conformation showed that the transient forces upstream of active promoters are large enough to drive the supercoil-sensitive far upstream element (FUSE) of the human c-myc into single-stranded DNA. An alternative non-B conformation of FUSE found in stably supercoiled DNA is not accessible dynamically. These results demonstrate that dynamic disturbance of DNA structure provides a real-time measure of ongoing genetic activity.

Base Sequence↗

PubMed2003

The pqrAB operon is responsible for paraquat resistance in Streptomyces coelicolor.

Paraquat (methyl viologen)-resistant mutants of Streptomyces coelicolor A3(2) that grew and sporulated normally in the presence of paraquat were isolated. Based on the positions of the mutant loci in the genetic map, we isolated the pqr (paraquat resistance) gene whose mutation (pqr501) caused a dominant paraquat-resistant phenotype. The pqr locus consists of two genes (pqrA and pqrB) that form a transcription unit. The pqrA gene encodes a protein with a TetR-like DNA-binding motif, and the pqrB gene encodes a putative efflux pump of the major facilitator superfamily. The pqr501 mutation was a base substitution changing arginine-18 to glutamine (R18Q) near the helix-turn-helix motif in PqrA. A pqrA null mutant exhibited similar paraquat resistance, and an increase in the amount of pqrA promoter-driven transcripts of about eightfold was observed for the pqrA501 mutant. These results suggest that PqrA is a negative regulator of its own operon. Deletion of the pqrAB operon caused cells to be very sensitive to paraquat, consistent with the prediction that PqrB may function as a paraquat-efflux pump. Purified PqrA protein specifically bound to the pqrA promoter region, whereas mutant R18Q protein did not, indicating that PqrA is a direct autoregulator of its own operon.

Amino Acid Sequence↗