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Abstract
Recognition and targeting of invaders by the prokaryotic CRISPR-Cas system depends on the acquisition of invader sequences within the host CRISPR locus. We are investigating the mechanisms of this unique biological process. The Cas1 and Cas2 proteins universal among the CRISPR-Cas systems have been genetically linked to adaptation, as has the 5-3 exonuclease Cas4 that is associated with some systems. The Pyrococcus furiosus genome encodes three CRISPR-Cas systems (Cmr Type III-B, Csa Type I-A, and Cst Type I-G), two Cas4 proteins (Cas4-1 and Cas4-2), as well as Cas1 and Cas2 proteins. In this work, in vivo interactions among these adaptation proteins were analyzed. This study indicates the existence of a complex that includes the Cas1 and Cas4-1 proteins, and evidence of Cas1 and Cas2 association. Moreover, we demonstrate that Cas1 associates with a plethora of non-Cas proteins and nucleic acids, which may be relevant to CRISPR-Cas adaptation.