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. At the left hand-side of the picture you can see the structure of the synthetic oligonucleotide used to stabilize the Cas4/Cas1 complex, whose structure is depicted at the right side of the figure. The structure of the complex was solved by CryoEM (PDB code: 7MID)
#molecularart ... #immolecular ... #crispr ... #cas ... #complex ... #pam ... #DNA ... #defense ... #bacteria ... #cryoem
Protein complex rendered with @proteinimaging and represented by @corelphotopaint
#molecularart ... #immolecular ... #crispr ... #cas ... #complex ... #pam ... #DNA ... #defense ... #bacteria ... #cryoem
Protein complex rendered with @proteinimaging and represented by @corelphotopaint
