枯草菌染色体の複製開始と制御の分子機構
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Recent progress in our studies on mechanism and regulation of initiation of chromosomal replication in Bacillus subtilis is reviewed. The origin of the chromosomal replication, OriC, is supposed to be composed of deoxyribonucleic acid (DNA) signals for initiation of autonomous replication and its regulation. A 245 bp sequence essential for autonomous replication has been isolated from OriC of E. coli. In contrast, attempts to isolate a similar sequence from B. subtilis has not been successful, suggesting that B. subtilis OriC is more complicated in structure and function than that of E. coli. To study structure and function of the B. subtilis OriC region, we first cloned some 50 kbp DNA in the origin region and determined the exact site of OriC in vivo within 1000 bp on each strand of the chromosome. The initiation site on each strand is located some 2 kb apart and replication proceeds inward to pass the other site, indicating the one strand be leading the other be lagging strand. Second, we have determined DNA sequence of 12 kbp around the OriC. Computer analysis of the sequence, determination of transcription in vivo by S-1 mapping and identification of gene products by the Maxi-cell method revealed 10 open reading frames (ORF=genes) which constitute 6 transcriptional units. The ORFs are identified by genetic evidence and comparison with known genes in E. coli. They are from left to right "RnpA"-"RpmH"-"DnaA"-"DnaN"-URF (unknown ORF) 71-RecF-URF52-GyrB-GyrA-RrnO. These genes are essential for cell growth involving in synthesis of DNA or ribonucleic acid, or in changes in DNA structure. Not only individual genes but also their organization is highly conserved between B. subtilis and E. coli. Two regulatory regions are found flanking "DnaA" gene. We concluded that they are B. subtilis OriC because 1. they contain 9 and 4 repeating sequences whose consensus sequence TTAT (C/A) CACA is identical to DnaA protein binding site in E. coli oriC, 2. transcription from within these regions parallels initiation of chromosomal replication. In contrast to E. coli OriC these regions do not replicate autonomously, instead inhibit plasmid replication when they are inserted into it. Difference in organization of OriC in relation to the regulatory gene "DnaA" may be responsible for the difference in OriC function between the two bacteria.
- 公益社団法人日本薬学会の論文
- 1985-11-25
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