Following up previous posts on this structure, remember that prokaryotes adapt to challenges from mobile genetic elements by integrating spacers derived from foreign DNA in the CRISPR array. Spacer insertion is carried out by the Cas1-Cas2 integrase complex. A substantial fraction of CRISPR-Cas systems use a Fe-S cluster containing Cas4 nuclease to ensure that spacers are acquired from DNA flanked by a protospacer adjacent motif (PAM) and inserted into the CRISPR array unidirectionally, so that the transcribed CRISPR RNA can guide target searching in a PAM-dependent manner. This structure demonstrated the molecular mechanism of Cas4-assisted PAM selection, spacer biogenesis and directional integration by type I-G CRISPR in Geobacter sulfurreducens, in which Cas4 is naturally fused with Cas1, forming Cas4/Cas1. Here you can see the whole Cas1/4-Cas2 complex bound to a synthetic target DNA. The structure of the complex was solved by CryoEM (PDB code: 7MI9)
#molecularart ... #immolecular ... #crispr ... #cas ... #complex ... #pam ... #DNA ... #defense ... #bacteria ... #cryoem
Protein complex rendered with @proteinimaging and represented with @corelphotopaint
#molecularart ... #immolecular ... #crispr ... #cas ... #complex ... #pam ... #DNA ... #defense ... #bacteria ... #cryoem
Protein complex rendered with @proteinimaging and represented with @corelphotopaint
