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Isolation and Characterization of a Second RNase H (RNase HII) of Escherichia coli K-12 Encoded by the rnhB Gene

Mitsuhiro Itaya
Proceedings of the National Academy of Sciences of the United States of America
Vol. 87, No. 21 (Nov., 1990), pp. 8587-8591
Stable URL: http://www.jstor.org/stable/2355587
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Isolation and Characterization of a Second RNase H (RNase HII) of Escherichia coli K-12 Encoded by the rnhB Gene
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Abstract

An additional RNase H (EC 3.1.26.4), RNase HII, has been isolated from Escherichia coli K-12. By screening a library of E. coli DNA for clones that suppressed RNase H deficiency of an E. coli rnh mutant, a clone was obained that produced a protein with RNase H activity. The overexpressed RNase HII protein in E. coli was purified to near homogeneity and exhibited a strong preference for the ribonucleotide moiety of RNA-DNA hybrid as substrate. The terminal 11 amino acids were determined and were identical to those predicted from the nucleotide sequence. The rnhB gene, which encodes RNase HII, was distinct from rnhA by its map position (4.5 min on E. coli genetic map, between lpxB and dnaE) and by the lack of significant amino acid sequence similarity. The presence of a second RNase H in E. coli indicates that multiple RNase H genes per genome is a general feature of a wide variety of organisms.

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