Figure 1.

Cells harboring plasmids expressing crRNA-like transcription units become resistant to phage infection. (A). Two ways of crRNA generation — by Cas6e-mediated endonucleolytic processing of pre-crRNA transcript of CRISPR array or by transcription termination on an intrinsic transcription terminator build upon the hairpin structure formed by the 3′-terminal repeat — are schematically shown. (B). CRISPR interference, calculated as efficiency of plaquing (EOP) of indicated phages on indicated cells lawns is shown. An EOP of 1 indicates that the number of plaques formed on lawns of cells with induced cas gene expression was the same as the number of plaques on lawns of cells which did not express any crRNA. For every non-cognate cell-phage combination, an EOP of 1 was observed.