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Ribonuclease H (RNase H) is a hydrolytic enzyme widely distributed in both prokaryotes and eukaryotes ([[Literature:85381|Johnson ''et al.'' 1986]]; [[Literature:18836|Doolittle ''et al.'' 1989]]). In ''Ty3/Gypsy'' and ''Retroviridae'' and other LTR retroelements this enzyme is encoded as a part of the pol polyprotein and constitutes the C-terminal end of the [[Reverse Transcriptase|Reverse Transcriptase]] (RT). RNase H is responsible for the hydrolysis of the original RNA template that is part of the RNA/DNA hybrid generated after the retrotranscription process in the viral life cycle.

The three dimensional (3D) structure of the HIV-1 RNase H is characterized by four or five α-helices and five β-sheets that interact aligning in parallel to conform the active site ([[Literature:16779|Davies ''et al.'' 1991]]). The activity of this enzyme normally requires the presence of divalent cations like Mg2+ or Mn2+ that bind to an active site constituted by a catalytic triad (Asp-443-Glu-478-Asp-498). These three residues have been proposed to be important in RNase H-mediated catalysis by HIV-1 RT ([[Literature:85507|Mizarhi ''et al.'' 1990]]; [[Literature:16779|Davies ''et al.'' 1991]]). Mutations in any of these resides inhibit the RNase H activity but have small effects on polymerase activity of the HIV-1 retrovirus ([[Literature:66949| Schatz ''et al.'' 1989]]; [[Literature:85507|Mizarhi ''et al.'' 1990]]; [[Literature:16779|Davies ''et al.'' 1991]]; [[Literature:17861|Destefano ''et al.'' 1994]]).

[[Image:ty3gypsy_rnasah_1.png|center]]
<center>HIV-1 RNase H 3D structure adapted from the PDB-file [http://www.ebi.ac.uk/pdbsum/1o1W 1o1W]</center>

[[Category:Retroelements]]

Ribonuclease H - Revision history

imported>Gydbwiki at 10:59, 22 April 2010