Reverse transcriptase activity innate to DNA polymerase I and DNA topoisomerase I proteins of Streptomyces telomere complex
- Departments of *Genetics and ‡Medicine, Stanford University School of Medicine, Stanford, CA 94305-5120
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Edited by Nicholas R. Cozzarelli, University of California, Berkeley, CA, and approved August 10, 2004 (received for review June 18, 2004)
Abstract
Replication of Streptomyces linear chromosomes and plasmids proceeds bidirectionally from a central origin, leaving recessed 5′ termini that are extended by a telomere binding complex. This complex contains both a telomere-protecting terminal protein (Tpg) and a telomere-associated protein that interacts with Tpg and the DNA ends of linear Streptomyces replicons. By using histidine-tagged telomere-associated protein (Tap) as a scaffold, we identified DNA polymerase (PolA) and topoisomerase I (TopA) proteins as other components of the Streptomyces telomere complex. Biochemical characterization of these proteins indicated that both PolA and TopA exhibit highly efficient reverse transcriptase (RT) activity in addition to their predicted functions. Although RT activity innate to other DNA-dependent DNA polymerases has been observed previously, its occurrence in a topoisomerase is unprecedented. Deletion mapping and sequence analysis showed that the RT activity of Streptomcyces TopA resides in a peptide region containing motifs that are absent from most bacterial topoisomerases but are highly conserved in a novel subfamily of eubacterial topoisomerases found largely in Actinobacteria. Within one of these motifs, and essential to the RT function of Streptomyces TopA, is an Asp-Asp doublet sequence required also for the RT activities of human immunodeficiency virus and eukaryotic cell telomerases.
Footnotes
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↵ § To whom correspondence should be addressed. E-mail: sncohen{at}stanford.edu.
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↵ † Present address: Department of Molecular Biology, Genencor International, Palo Alto, CA 94304.
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This paper was submitted directly (Track II) to the PNAS office.
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Abbreviations: RT, reverse transcriptase; Tap, telomere-associated protein.
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See Commentary on page 14307.
- Copyright © 2004, The National Academy of Sciences
