Department of microbiology and molecular genetics
Faculty profile
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Junichi Ryu 11021 Campus Street |
- PhD Tokyo Metropolitan University (Tokyo), 1978
- Visiting professor, University of Basel, Basel, Switzerland, 1996-1997
- Biotechnology masters program coordinator, 1997
- Current research interests
- Recent publications
- Teaching
- Coomunity activity - Japan Club
Distribution of type I restriction enzymes in bacteria
Restriction enzymes and the corresponding modification methylase (R-M systems) are unique to bacteria. Based on the cutting mode, restriction endonucleases are divided into three types (I to III). Among those, type II restriction enzymes are the most popular (about 3,000 has been known). Some of those have become essential tools in gene manipulation. On the other hand, our knowledge concerned with the distribution on type I enzymes are sketchy. Less than thirty type I enzymes were so far reported from mainly E. coli and S. typhimurium. Recently, however, complete DNA sequence of several bacteria were revealed through various Genome Projects and many type I homologues were found. The results suggest a wide spread of type I restriction enzymes.
To identify presence of restriction enzyme in bacteria, a new simple method was developed in our laboratory. This method is based on plasmid transformation. A computer program was also developed to identify the recognition sequence.
In the past, we have studied two new restriction-modification systems of Klebsiella pneumoniae, which we named KpnAI and KpnBI. Recently, we have cloned and sequenced the entire sequence of KpnAI genes as well as the gene for the restriction subunit of the KpnBI. The KpnAI was identified as a first type I restriction enzyme in this species. Search for the recognition sequences of KpnAI and KpnBI are underway.
Regulation of type I restriction enzymes in enteric bacteria
The genes code for type I restriction endonuclease can be transferred to the bacteria which do not contain any corresponding methylase activity. Since the restriction endonuclease transferred to the recipient is supposed to cut the unmodified recipient chromosome, this successful "establishment" of the type I restriction enzymes poses an intriguing question how the restriction and modification genes are expressed after the transfer. Using E. coli cells, we showed that the expression is controlled by regulating the timing of the expression of restriction activity. We also showed that the level of restriction subunit is controlled at the post translational level. A key factor was identified by identifying a mutant which does not have this control. We named this key gene "hsdC". More recently we found that this key mutation is suppressed by a gene product of ClpX, a serine protease. The mechanism of this suppression is now under the study.
Expression of restriction enzymes in eukaryotic cells
Restriction enzymes are exclusively identified in bacteria. Since they destroy the foreign DNA and contribute to preserve own species, it sometimes compared to the immune system in eukaryote. Thus, it is interesting to see that whether the enzymes work in eukaryotic cells in vivo. If they work successfully as they do in bacteria, restriction endonuclease and the corresponding methylase may provide a protection from foreign invaders such as viruses. This idea will lead us to a possibility that these enzymes can be used as either protective measure against viruses or a tool for gene therapy.
Click on the 
symbol beside the reference to read the corresponding abstract.
Lee, N.S., Rutebuka, O., Arakawa, T., Bickle, T. and Ryu, J. 1997. KpnAI, a New Type I Restriction-Modification System in Klebsiella pneumoniae. J. Mol. Biol. 271:342-348.
Valinluck, B. Lee, N.S. and Ryu, J. 1995. A new restriction-modification system KpnBI, recognized in Klebsiella pneumoniae. Gene 167:59-62.
Prakash-Cheng, A and Ryu, J. 1993. Delayed expression of in vivo restriction activity following conjugal transfer of E. coli hsdK (restriction-modification) genes. J. Bacteriol. 175:4905-4906.
Prakash-Cheng, A., Chung and Ryu, J. 1993. The expression and regulation of hsdK genes after conjugative transfer. Mol. Gen. Genet. 241:491-496.
Main teaching responsibility:
CMBL502 Molecular Biology of Prokaryotes and Eukaryotes, Coordinator
Community activities - Japan Club
Loma Linda Japan Club was formed in 1992 to provide a comprehensive service to the Japanese researchers in Loma Linda University. The Club publishes a Loma Linda Guide Book and an annual newsletter in Japanese and provides various information necessary for initial setting and the living in Loma Linda and the vicinity. The Internet homepage was opened since 1997. Although our primary goal is to serve the local Japanese community, the Club will provide a similar service, when requested, to students and other people in the community.
School of Medicine - Graduate School - Loma Linda University
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