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Nucleic Acids Research Advance Access originally published online on August 5, 2008
Nucleic Acids Research 2008 36(16):5212-5220; doi:10.1093/nar/gkn494
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Nucleic Acids Research, 2008, Vol. 36, No. 16 5212-5220
© 2008 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Nucleic Acid Enzymes

A comparative analysis of two conserved motifs in bacterial poly(A) polymerase and CCA-adding enzyme

Andrea Just, Falk Butter, Michelle Trenkmann, Tony Heitkam, Mario Mörl and Heike Betat*

Institute for Biochemistry, University of Leipzig, Brüderstr. 34, 04103 Leipzig, Germany

*To whom correspondence should be addressed. Tel: +49 341 9736993; Fax: +49 341 9736919; Email: hbetat{at}uni-leipzig.de

Received June 25, 2008. Revised July 15, 2008. Accepted July 16, 2008.

Showing a high sequence similarity, the evolutionary closely related bacterial poly(A) polymerases (PAP) and CCA-adding enzymes catalyze quite different reactions—PAP adds poly(A) tails to RNA 3'-ends, while CCA-adding enzymes synthesize the sequence CCA at the 3'-terminus of tRNAs. Here, two highly conserved structural elements of the corresponding Escherichia coli enzymes were characterized. The first element is a set of amino acids that was identified in CCA-adding enzymes as a template region determining the enzymes' specificity for CTP and ATP. The same element is also present in PAP, where it confers ATP specificity. The second investigated region corresponds to a flexible loop in CCA-adding enzymes and is involved in the incorporation of the terminal A-residue. Although, PAP seems to carry a similar flexible region, the functional relevance of this element in PAP is not known. The presented results show that the template region has an essential function in both enzymes, while the second element is surprisingly dispensable in PAP. The data support the idea that the bacterial PAP descends from CCA-adding enzymes and still carries some of the structural elements required for CCA-addition as an evolutionary relic and is now fixed in a conformation specific for A-addition.


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