engleski

The interaction between HtpG and Cas3 proteins on activity of the Escherichia coli type I-E CRISPR-Cas system

CRISPR (clustered regularly interspaced short palindromic repeats) and its associated Cas proteins provide many bacteria and archaea with a defence mechanism by RNA mediated targeting of invading genetic elements. Escherichia coli type I-E CRISPR-Cas system detects invading DNA by a "Cascade" nucleoprotein surveillance complex that contains CRISPR RNA (crRNA) bound within that recognizes sequences on invader DNA flanked by “Protospacer Adjacent Motifs” (PAMs). This triggers R-loop formation and binding of Cas3 helicase-nuclease that degrades invader DNA. Previous studies showed that cells lacking H-NS have elevated levels of Cascade and crRNA transcripts and are resistant to infection by phage vir if they contain appropriate anti-lambda spacer. Surprisingly, resistance was strongly dependent on post-infection temperature of incubation: at 30°C E. coli hns cells containing anti-lambda spacer were fully resistant to phage attack but were sensitive if incubated at 37°C. In this work we investigated this effect of temperature on CRISPR defence, identifying that although PAM sequences were important for maximal resistance to phage at 30°C, resistance to vir at 37°C relied on increased expression of Cas3 or HtpG, in hns cells. This suggests that levels of active Cas3 are limiting to support efficient resistance to phage at 37°C in hns cells. Significantly, we describe the new identification that cas3 is also under transcriptional control by H-NS but that this is exerted only in stationary phase cells.

CRISPR-Cas; Cas3; HtpG; E. coli; H-NS

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