Biomedical subjects

Junghyun Park

Publications and source records attributed to Junghyun Park.

6 recordsLinked to original sources

PubMed2005

Frames of reference for saccadic command tested by saccade collision in the supplementary eye field.

In what frame of reference does the supplementary eye field (SEF) encode saccadic eye movements? In this study, the "saccade collision" test was used to determine whether a saccade electrically evoked in the monkey's SEF is programmed to reach an oculocentric goal or a nonoculocentric (e.g., head or body-centered) goal. If the eyes start moving just before or when an oculocentric goal is imposed by electrical stimulation, the trajectory of the saccade to that goal should compensate for the ongoing movement. Conversely, if the goal imposed by electrical stimulation is nonoculocentric, the trajectory of the evoked saccade should not be altered. In head-fixed experiments, we mapped the trajectories of evoked saccades while the monkey fixated at each of 25 positions 10 degrees apart in a 40 x 40 degrees grid. For each studied SEF site, we calculated convergences indices and found that "convergent" and "nonconvergent" sites were separately clustered: nonconvergent rostral to convergent. Then, the "saccade collision" test was systematically applied. We found compensation at sites where saccades were of the nonconvergent type and practically no compensation at sites where saccades were of the convergent type. The results indicate that the SEF can encode saccade goals in at least two frames of reference and suggest a rostrocaudal segregation in the representation of these two modes.

Adaptation, Ocular↗

PubMed2005

Functional dissection of HCMV US11 in mediating the degradation of MHC class I molecules.

The human cytomegalovirus (HCMV) gene product US11 dislocates MHC I heavy chains from the endoplasmic reticulum (ER) and targets them for proteasomal degradation in the cytosol. To identify the structural and functional domains of US11 that mediate MHC class I molecule degradation, we constructed truncated mutants and chimeric proteins, and analyzed these to determine their intracellular localization and their ability to degrade MHC class I molecules. We found that only the luminal domain of US11 was essential to confer ER localization to the protein but that the ability to degrade MHC class I molecules required both the transmembrane domain and the luminal domain of US11. By analyzing a series of point mutants of the transmembrane domain, we were also able to identify Gln(192) and Gly(196) as being crucial for the functioning of US11, suggesting that these residues may play a critical role in interacting with the components of the protein degradation machinery.

Amino Acids↗

PubMed2005

pIH01, a small cryptic plasmid from Leuconostoc citreum IH3.

A small cryptic plasmid pIH01 from Leuconostoc citreum IH3 was characterized. This 1.8-kb sized plasmid contains single open reading frame that encodes a RepC class protein (342 amino acids) and a conserved pT181-type double strand origin, suggesting a rolling circle replication mode. This putative replicase protein shows the highest similarity to a replicase from pFR18 plasmid of Leuconostoc mesenteroides FR52 (64% identity), one of the pT181-type rolling circle plasmid family and contains a strictly conserved RepC-type active site sequence of pT181 family. A shuttle vector that was developed on the basis of this cryptic plasmid by insertion of both erythromycin resistance gene (ermC) from pE194 and Escherichia coli ColE1 origin was able to transform Leuconostoc strains, Lactobacillus plantarum, and Lactococcus lactis. Therefore, pIH01 derivative plasmids might be useful for the manipulation of Leuconostoc strains.

Amino Acid Sequence↗

PubMed2003

Voluntary action expands perceived duration of its sensory consequence.

When we look at a clock with a hand showing seconds, the hand sometimes appears to stay longer at its first-seen position than at the following positions, evoking an illusion of chronostasis. This illusory extension of perceived duration has been shown to be coupled to saccadic eye movement and it has been suggested to serve as a mechanism of maintaining spatial stability across the saccade. Here, we examined the effects of three kinds of voluntary movements on the illusion of chronostasis: key press, voice command, and saccadic eye movement. We found that the illusion can occur with all three kinds of voluntary movements if such movements start the clock immediately. When a delay is introduced between the voluntary movement and the start of the clock, the delay itself is overestimated. These results indicate that the illusion of chronostasis is not specific to saccadic eye movement, and may therefore involve a more general mechanism of how voluntary action influences time perception.

Adult↗

PubMed2003

Spatial localization precedes temporal determination in visual perception.

The temporal order of two spots of light successively appearing in the dark, just before a saccade, influences their perceived spatial relation. Both spots are mislocalized in the saccade direction--the second more so than the first--because mislocalization grows as time elapses from stimulus to saccade onset. On the other hand, the perceived order of the two spots may be altered if the second spot is at the focus of spatial attention. How would these illusory perceptions of space and time interact when they are brought to play together? Could they be independent or could one perception depend on the other? Here we show that perceived location of stimuli is not affected by illusory temporal order, whereas perceived temporal order is affected by misperceived location. The results suggest that the brain processes spatial location of visual stimuli before processing their temporal order.

Attention↗

PubMed2002

Hantaan virus enters cells by clathrin-dependent receptor-mediated endocytosis.

The cellular entry of Hantaan virus (HTN) occurs through interactions with beta(3) integrins as cellular receptors. However, the process of HTN infection following attachment to the cell surface is not well understood. Our data indicate that overexpression of a dominant-negative mutant dynamin inhibits HTN internalization and that compounds that block clathrin- but not caveolae-dependent endocytosis also reduce HTN infectivity. In addition, we show that HTN colocalizes with the clathrin heavy chain but not with caveolae. At the early phase of infection HTN colocalizes with EEA-1, an early endosome marker, and later, HTN colocalizes with LAMP-1, a lysosome marker. Cells treated with lysosomotropic agents are largely resistant to infection, suggesting that a low-pH-dependent step is required for HTN infection. These findings demonstrate that HTN enters cells via the clathrin-coated pit pathway and uses low-pH-dependent intracellular compartments for infectious entry.

Animals↗