< NINS ASTROBIOLOGY CENTER >LABORATORY OF BIOLOGICAL DIVERSITYJOHZUKA Group
Assistant Professor:
Technical Staff:changes from a simple loop into a complicated twisted shapeas the cell cycle progresses from metaphase to anaphase.

JOHZUKA, Katsuki
ISHINE Naomi

I. Condensin-dependent chromatin folding

Chromosome condensation is a basic cellular process thatensures the faithful segregation of chromosomes in bothmitosis and meiosis. Any abnormality in this process leads tosegregation errors or aneuploidy, which results in cell death.
Chromosome condensation is mainly achieved by condensin, a hetero-pentameric protein complex, widely conserved
across a variety of organisms ranging from yeast to humans.
Despite its conservation and importance in chromosome
dynamics, it is not fully understood how condensin works.
Our aim is to understand the mechanism and regulation of chromosome condensation. To this end, we havebeen studying the role of condensin in the budding yeast
Saccharomyces cerevisiae. We have found that condensin
specifically binds to the RFB site located within the rDNA
repeat. To date, the best characterized condensin binding
region is the rDNA repeat on the right arm of chromosome
XII in budding yeast. We further discovered the multiple
protein network required to recruit condensin to the RFBsite.
The RFB site, which consists of a ~150bp DNA sequence,
functions as a cis-element for the recruitment of condensin
to chromatin in the yeast genome. If the RFB site is inserted
into an ectopic chromosomal locus, condensin can associatewith the ectopic RFB site. To explore the role of condensin
in chromosome organization, we have constructed a strain
in which two RFB sites are inserted into an ectopic chromosome arm with an interval of 15kb distance in the cell with acomplete deletion of chromosomal rDNA repeat. Using thisstrain, condensin-dependent chromatin interaction between
two RFBs was examined by chromosome conformation
capture (3C) assay. We discovered the condensin-dependent
chromatin interaction between the two RFB sites on the chromosome arm. This result indicates that condensin plays a rolein chromatin interaction between condensin binding sites,
and this interaction leads to the creation of a chromatin loop
between those sites (Figure 1). It is thought that condensindependent chromatin folding is one of the basic molecular
processes of chromosome condensation. During the cell
cycle stages, the RFB - RFB interaction signal increases in
metaphase and reaches its maximum level in anaphase. In
addition to the RFB - RFB interaction, the chromatin interactions between the internal regions of the two RFBs increases
in anaphase. Thus, the configuration of chromatin fiber

Figure 1. A Schematic model of chromosome condensation. Condensin
makes chromatin interactions between adjacent binding sites (RFB, forexample). This leads to a folding of chromatin fibers between the sites, asa basic process of chromosome condensation.

II. Plasma-induced cellular responses

Plasma is an ionized gas, which consist of ions and electrons and is extremely reactive. Our question is to understandthe effect of the plasma on living organisms.
We have developed a new plasma irradiation device that cancontrol the temperature to the optimal growth temperatureof cells, and have developed a system to study the effects ofdirect plasma exposure to cells without heat stress (Figure2). Using yeast, S.cerevisiae, it was found that direct plasma
exposure treatment increases lethality as the processing timeincreases (Figure 3). Furthermore, a plasma-resistant mutant
was isolated and the causative gene responsible for plasmaresistance was identified. We are studying functional analysisof the gene to understand the molecular mechanisms of thecellular responses to plasma.

Figure 2. Schematic diagram of atomosperic pressure plasma irradiation
device (left). Direct plasma irradiation experiment (right).

Figure 3. wild-type (upper panels) and plasma-resistant mutant (lower panels)

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