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Molecular Mechanisms of the Bacterial "Immunity" System CRISPR-Cas

The CRISPR-Cas system provides bacteria and archaea an adaptive and heritable immunity against phages or plasmids. Consisting of a CRISPR locus and CRISPR-associated (Cas) proteins, the system allows the specific recognition and elimination of the invading foreign DNA by an RNA-guided DNA-interference mechanism. The immunization against the foreign DNA occurs by the incorporation of short pieces of the invading DNA into the CRISPR locus (stage 1), from which small CRISPR RNAs (crRNAs) are produced through transcription of the locus followed by processing of the precursor crRNA (stage 2). In association with Cas proteins, the crRNAs mediate the destruction of the target DNA (stage 3). Ten different CRISPR-Cas systems are known, constituted by the members of more than 40 different Cas protein families. Most of the Cas proteins are uncharacterized and the mechanisms behind the individual stages are unclear.


CRISPR research has become one of the most innovative and exciting fields within Microbiology, with broad potential for applications in medicine and biotechnology. Recent findings have revolutionized the generation of transgenic organisms: Engineered RNA-loaded CRISPR nucleases are active in eukaryotic cells and have been used 1. to generate transgenic organisms with multiple selective genome mutations but also 2. to cure viral infections in cell cultures. The technology has been applied in several eukaryotes (e.g. Drosophila, C. elegans, Zebrafish, human embryonic stem cells, plants), thus providing an efficient and precise tool for targeted genome engineering in increasing number of model organisms.

Research Interests and Techniques

Our aim is to elucidate the molecular mechanisms behind the CRISPR-Cas systems with special focus on:

1. Charakterisierung der regulatorischen Komponenten der TranCharacterization of the regulatory components for the transcription and processing of the crRNAs [1-4].skription und Prozessierung von crRNAs [1-4].

2.   Analysis of Cascade components and crRNA-mediated recognition of target DNA by the Cascade complex [5].

3.    Unraveling the mechanism of foreign DNA selection and incorporation into the CRISPR array [6-8].

We employ a broad range of microbiological, biochemical and molecular biological methods (ranging from modified mobility shift assays to several high-resolution footprint techniques, gene expression analyses and atomic force microscopy) to understand the biological processes behind this bacterial immune system against viruses and other mobile genetic elements.

Pul 2

[1] Pul Ü et al. (2010) Mol. Microbiol 75:1495-1512

[2] Westra E R, Pul Ü et al. (2010) Mol. Microbiol. 77:1380-1393

[3] Stratmann T, Pul Ü et al. (2012) Mol. Microbiol. 83:1109-1123

[4] Arslan Z et al. (2013) RNA Biol. 10:708-715

[5] Jore et al. (2011) Nat. Struct. Mol. Biol. 18:529–536

[6] Ellinger et al. (2012) J. Struct. Biol. 178: 350-62

[7] Arslan Z et al. (2013) Nucl Acids Res 41:6347-6359