Protein Engineering, Vol. 13, No. 12, 881-886,
December 2000
© 2000 Oxford University Press
Efficient cleavage of RNA at high temperatures by a thermostable DNA-linked ribonuclease H
Department of Material and Life Science, Graduate School of Engineering, Osaka University, 21, Yamadaoka, Suita, Osaka 565-0871, Japan
To construct a DNA-linked RNase H, which cleaves RNA site-specifically at high temperatures, the 15-mer DNA, which is complementary to the polypurine-tract sequence of human immunodeficiency virus-1 RNA (PPT-RNA), was cross-linked to the unique thiol group of Cys135 in the Thermus thermophilus RNase HI variant. The resultant DNA-linked enzyme (d15-C135/TRNH), as well as the d15-C135/ERNH, in which the RNase H portion of the d15-C135/TRNH is replaced by the Escherichia coli RNase HI variant, cleaved the 15-mer PPT-RNA site-specifically. The mixture of the unmodified enzyme and the unlinked 15-mer DNA also cleaved the PPT-RNA but in a less strict manner. In addition, this mixture cleaved the PPT-RNA much less effectively than the DNA-linked enzyme. These results indicate that the cross-linking limits but accelerates the interaction between the enzyme and the DNA/RNA substrate. The d15-C135/TRNH cleaved the PPT-RNA more effectively than the d15-C135/ERNH at temperatures higher than 50°C. The d15-C135/TRNH showed the highest activity at 65°C, at which the d15-C135/ERNH showed little activity. Such a thermostable DNA-linked RNase H may be useful to cleave RNA molecules with highly ordered structures in a sequence-specific manner.
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