Reverse transcriptase nuclease activity

Although many enzymes that are active in the processing of nucleic acids, such as nucleases, DNA polymerases, or reverse transcriptases, have acidic residues in the active sites and require divalent cations for activity, such cations have been repotted only for a few published structures. One published structure of reverse transcriptase from Moloney murine leukemia virus, (MMLV RT) shows a single metal bound in the active site (15), whereas none of the available structures of HIV-1 RT show bound metals. In addition, the structures of MMLV RT and E. coli RNase H with bound metals have been solved at a lower resolution than the... 

P or 5 -P products. Many polymerases, including reverse transcriptases, also exhibit intrinsic nuclease activities with widely varying reaction and substrate specificities, which makes the rational division of nucleases even more complex. 

Initially discovered in extracts of calf thymus as a contaminating enzyme during the purification of RNA polymerase (1,2), RNase H has since been found almost ubiquitously in lower and higher eukaryotes as well as in prokaryotes. A single cell type may have one or more species of RNases H residing in the cell nucleus and/or cytosol. Some RNases H have a single ribonucleolytic reaction specificity, whereas others are associated with DNA polymerase activities. Cellular RNases H, for example, from E. coli and calf thymus, are endonucleases the retroviral reverse transcriptase-associated RNases H can function as both exo- and endoribo-nucleases depending on the type of substrates available. 

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