寒冷バイオシステム研究センター

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Saitoh, Y., Miyagi, S., Ariga, H., Tsutsumi, K. (2002)
Functional domains involved in the interaction between Orc1 and transcriptional repressor AlF-C that bind to an origin/promotor of the rat aldlase B gene.
Nucleic Acids Res. 30: 5205-5212.
The promoter of the rat aldolase B (AldB) gene functions in vivo as an origin of DNA replication in the cells in which transcription of the gene is repressed. Previously, we identified two closely related DNA-binding proteins, AlF-C1 and AlF-C2, which repressed of the AldB gene promoter. We also reported that the binding site of these proteins, site C, is one of the necessarily required DNA elements of the AldB gene origin/promoter for autonomously replicating activity in transfected cells. In the present study, we show that AlF-C1 and AlF-C2 directly bind to Orc1, a subunit of the origin recognition complex (ORC). Deletion analyses revealed a functional domain in AlF-C2 for binding to Orc1, which located separately from the DNA-binding domain. In addition, we found a novel protein-interacting domain in Orc1 required for binding of AlF-C2, which was conserved in human, mouse and Chinese hamster, but not in Drosophila, flog and yeast. Thus, it is assumed that in mammalian cells, sequence-specific DNA binding proteins are involved in recruiting ORC to regulate replication initiation and/or transcription repression.

Wang, Y., Saitoh, Y., Hidaka, S., Sato, T., Tsutsumi, K. (2002)
Replication of plastid DNA.
Recent Res. Devel. Plant Biol. 2: 33-48.
Plastid is a name for organelles derived from a progenitor proplastid. The proplastid in immature cells of meristematic tissues differentiates with the host cells to various organelles including chloroplast, chromoplast, amyloplast, and leucoplast. Consequently, all these organelles contain the same genome DNA (plastid DNA, ptDNA). To maintain plastid lineages division of plastid and replication of ptDNA must take place. Recent reports showed that FtsZ and MinD, homologues of bacterial proteins required for cell division, play important roles in plastid division. In vivo and in vitro studies have mapped origins of ptDNA replication in several plant and algal species, and proposed at least two types of replication, D-loop-started unidirectional replication and rolling circle replication. These studies further suggested that replication initiation does not depend solely on the primary structure. Copy number of plastid and ptDNA varies depending on developmental stages and physiological status of host cells. These regulations might overlap those of initiation and made of replication.

Yoshino, M., Kanazawa, A., Tsutsumi, K., Nakamura, I., Takahashi, K., Shimamoto Y. (2002)
Structural Variation Around the Gene Encoding the α Subunit of Soybean β-Conglycinin and Correlation with the Expression of the α Subunit.
Breeding Science 52: 285-292.
We have identified two genes, located approximately 2.5 kb apart in the soybean genome, that are closely related to the α subunit of β-conglycinin. One of these genes has been shown to encode the α subunit and the other is very similar to the α subunit gene (referred to as the "α-related gene"). To determine whether the latter α-related gene expresses the α subunit, the structure of the chromosomal DNA region that contains the two genes was compared among soybean varieties exhibiting different expression levels of the subunit protein. We observed the presence of deletions of the α subunit and α-related genes in some varieties. In the naturally occurring variety Keburi, which accumulates the α subunit protein, the entire α-related gene was deleted in addition to the previously known deletion of the α' subunit gene. On the contrary, the α subunit gene was deleted in Monshidou Gong 503 and Kari-kei 434. These structural analyses revealed that the α-related gene expresses the α subunit at least in Moshidou Gong 503 and Kari-kei 434. These two varieties do not harbour the α subunit gene, but carry the intact α-related genes and still express the α subunit.