Our group is interested in the biochemistry and evolution of RNA-directed nucleotidyltransferases, RNA editing events as well as the generation of RNA or DNA aptamers directed against specific bacterial surface structures.

1. tRNA Nucleotidyltransferases

These nucleotidyltransferases add the nucleotide triplet C-C-A to the 3’-end of tRNAs, where this sequence represents the site for aminoacylation. Using a single nucleotide binding pocket in the N-terminal catalytic core, the CCA-adding enzymes incorporate two C residues and subsequently switch their specificity towards A addition. In the NTP binding site, a set of highly conserved amino acids forms Watson-Crick-like hydrogen bonds to the incoming nucleotides (amino acid template). A reorientation of these residues is responsible for the mentioned change in nucleotide specificity.


Besides the CCA-adding enzymes, closely related nucleotidyltransferases with partial activities exist, adding only two C residues (CC-adding enzymes) or the terminal A (A-adding enzymes). In addition, poly(A) polymerases are further close relatives of the CCA-adding enzymes. Using a reciprocal exchange strategy, we are trying to dissect individual enzyme regions and determine their specific functions to understand the molecular basis for the specificity of the individual types of enzymes. In the case of CC-adding enzymes, we could demonstrate that a hinge region required for the specificity switch of the amino acid template is missing due to a small deletion. When such a hinge element is reinserted, the CC-adding enzyme regains the full CCA-adding activity.


With a similar strategy, we are identifying functional domains in a series of other related nucleotidyltransferases and poly(A) polymerases.

2. tRNA Editing

In many organisms, some tRNA genes carry 3’-terminal deletions in the acceptor stem, resulting from overlaps with downstream located genes. In a posttranscriptional editing event, the missing nucleotides are inserted into the truncated tRNAs, generating complete and functional transcripts. Using a model tRNA editing reaction in S. cerevisiae, we are investigating the evolution of editing activities. Our results indicate that particularly the promiscuous nucleotide inserting activities involved in RNA quality control meet the requirements to evolve into such editing enzymes. Using in vivo as well as in vitro experiments, we could identify the yeast TRAMP4 complex as a first example of such a possible editing candidate enzyme.

3. Aptamers

Systematic Evolution of Ligands by Exponential Enrichment (SELEX) is an in vitro process that allows isolating nucleic acids which bind to target molecules at high specificity, comparable to antibodies. We are using this strategy to generate RNA and DNA aptamers that recognize and bind specific bacterial surface structures. These aptamers will be used as diagnostic as well as therapeutic tools for microbiological and clinical investigations.

letzte Änderung: 17.08.2016


Prof. Dr. Mario Mörl
Institut für Biochemie
Brüderstraße 34
D-04103 Leipzig

Telefon: +49 341 97-36910
Telefax: +49 341 97-36919

Petra Hartung

Telefon: +49 341 97-36910
Telefax: +49 341 97-36919