Question 1

Does a CRISPR locus mean an active system?

Accepted Answer

No. Many arrays are carried without detectable expression or interference under standard conditions, and some cas genes are inactivated. Confirming transcription and demonstrating interference against a matched target is what converts a sequence observation into a functional claim, and it is a step frequently skipped.

Question 2

How should spacer matches be judged?

Accepted Answer

With criteria fixed before searching, including minimum identity and length, and with an estimate of how many matches arise by chance at those settings. Short spacers match database sequence readily, so a hit count without a random expectation gives no sense of whether the signal is meaningful.

Question 3

What controls does an interference assay need?

Accepted Answer

A strain lacking the matching spacer, or a plasmid lacking the protospacer, run alongside. Transformation efficiency varies for reasons unrelated to cleavage, so reduced colony counts alone do not demonstrate interference. Including the target-free comparison is what makes the difference attributable to the system.

Question 4

Should the system be classified formally?

Accepted Answer

Where possible, yes, using an established classification scheme and citing the version applied. Type and subtype assignment communicates a great deal about expected mechanism, and schemes have been revised, so naming the one used avoids ambiguity when the classification later changes.

Question 5

How are anti-CRISPR proteins accounted for?

Accepted Answer

As part of the system rather than as an inconvenience. Phages carrying anti-CRISPR genes evade interference, so a strain showing no protection may still have a functional system facing an evasive phage. Checking the phage genome for known anti-CRISPR families before concluding the system is inactive saves misinterpretation.

Question 6

What makes self-targeting useful antimicrobially?

Accepted Answer

Programming the system against a sequence in the host chromosome or a resistance plasmid causes cleavage the cell cannot repair readily, which kills or cures selectively. The practical obstacle is delivery into the target population, and this usually limits progress more than the targeting design does.

Question 7

Are escape mutants expected?

Accepted Answer

Routinely. Single changes in the protospacer or its adjacent motif abolish recognition, so populations under interference pressure produce escapers quickly. Sequencing survivors rather than treating them as failures often provides the most informative data about recognition requirements in the system being studied.

Microbiology

Microbiology

Research Frontiers in CRISPR-Cas Systems in Bacterial Defense