Identification of the Genes Encoding Mn2+-Dependent RNase HII and Mg2+-Dependent RNase HIII from Bacillus subtilis: Classification of RNases H into Three Families

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• 作者：Naoto Ohtani ; Mitsuru Haruki ; Masaaki Morikawa ; Robert J. Crouch ; Mitsuhiro Itaya ; and Shigenori Kanaya
• 刊名：Biochemistry
• 出版年：1999
• 出版时间：January 12, 1999
• 年：1999
• 卷：38
• 期：2
• 页码：605 - 618
• 全文大小：255K
• 年卷期：v.38,no.2(January 12, 1999)
• ISSN：1520-4995

文摘

Database searches indicated that the genome of Bacillus subtilis contains three different genesencoding RNase H homologues. The ypdQ gene encodes an RNase HI homologue with 132 amino acidresidues, whereas the rnh and ysgB genes encode RNase HII homologues with 255 and 313 amino acidresidues, respectively. RNases HI and HII show no significant sequence similarity. These genes wereindividually expressed in Escherichia coli; the recombinant proteins were purified, and their enzymaticproperties were compared with those of E. coli RNases HI and HII. We found that the ypdQ gene productshowed no RNase H activity. The 2.2 kb pair genomic DNA containing this gene did not suppress theRNase H deficiency of an E. coli rnhA mutant, indicating that this gene product shows no RNase Hactivity in vivo as well. In contrast, the rnh (rnhB) gene product (RNase HII) showed a preference forMn²⁺, as did E. coli RNase HII, whereas the ysgB (rnhC) gene product (RNase HIII) exhibited a Mg²⁺-dependent RNase H activity. Oligomeric substrates digested with these enzymes indicate similar recognitionof these substrates by B. subtilis and E. coli RNases HII. Likewise, B. subtilis RNase HIII and E. coliRNase HI have generated similar products. These results suggest that B. subtilis RNases HII and HIIImay be functionally similar to E. coli RNases HII and HI, respectively. We propose that Mn²⁺-dependentRNase HII is universally present in various organisms and Mg²⁺-dependent RNase HIII, which may haveevolved from RNase HII, functions as a substitute for RNase HI.