Biomedical subjects

Ulrich F Müller

Publications and source records attributed to Ulrich F Müller.

3 recordsLinked to original sources

PubMed2005

TbMP42, a protein component of the RNA editing complex in African trypanosomes, has endo-exoribonuclease activity.

RNA editing in trypanosomatids is catalyzed by a high molecular mass RNP complex, which is only partially characterized. TbMP42 is a 42 kDa protein of unknown function that copurifies with the editing complex. The polypeptide is characterized by two Zn fingers and a potential barrel structure/OB-fold at its C terminus. Using recombinant TbMP42, we show that the protein can bind to dsRNA and dsDNA but fails to recognize DNA/RNA hybrids. rTbMP42 degrades ssRNA by a 3' to 5' exoribonuclease activity. In addition, rTbMP42 has endoribonuclease activity, which preferentially hydrolyzes non-base-paired uridylate-containing sequences. Gene silencing of TbMP42 inhibits cell growth and is ultimately lethal to the parasite. Mitochondrial extracts from TbMP42-minus trypanosomes have only residual RNA editing activity and strongly reduced endo-exoribonuclease activity. However, all three activities can be restored by the addition of rTbMP42. Together, the data suggest that TbMP42 contributes both endo- and exoribonuclease activity to the editing reaction cycle.

Animals↗

PubMed2003

Substrate 2'-hydroxyl groups required for ribozyme-catalyzed polymerization.

A polymerase ribozyme has been generated that uses nucleoside triphosphates to elongate an RNA primer by the successive addition of nucleotides complementary to an RNA template. Its polymerization is accurate, with an average error rate less than 3%, and it is general in terms of the sequence and the length of the primer and template RNAs. To begin to understand how the substrate contacts contribute to this accurate and general activity, we investigated which primer and template 2'-hydroxyl groups are involved in substrate recognition. We identified eight positions where 2'-deoxy substitutions can influence polymerization kinetics. All eight are within five nucleotides of the primer 3' terminus. Some, but not all, of the 2'-deoxy effects appear to be sequence dependent. These results begin to build a picture of how the polymerase ribozyme recognizes its substrates.

Catalysis↗

PubMed2002

Mechanism of the gBP21-mediated RNA/RNA annealing reaction: matchmaking and charge reduction.

The guide RNA-binding protein gBP21 has been characterized as a mitochondrial RNA/RNA annealing factor. The protein co-immunoprecipitates with RNA editing ribonucleoprotein complexes, which suggests that gBP21 contributes its annealing activity to the RNA editing machinery. In support of this view, gBP21 was found to accelerate the hybridization of cognate guide (g)RNA/pre-edited mRNA pairs. Here we analyze the mechanism of the gBP21-mediated RNA annealing reaction. Three possible modes of action are considered: chaperone function, matchmaker function and product stabilization. We conclude that gBP21 works as a matchmaker by binding to gRNAs as one of the two RNA annealing reactants. Three lines of evidence substantiate this model. First, gBP21 and gRNAs form a thermodynamically and kinetically stable complex in a 1 + 1 stoichiometry. Secondly, gRNA-bound gBP21 stabilizes single-stranded RNA, which can be considered the transition state in the annealing reaction. Thirdly, gBP21 has a low affinity for double-stranded RNAs, suggesting the release of the annealed reaction product after the hybridization step. In the process, up to six ionic bonds are formed between gBP21 and a gRNA, which decreases the net negative charge of the RNA. As a consequence, the electrostatic repulsion between the two annealing reactants is reduced favoring the hybridization reaction.

Adsorption↗