assay based on engineered selectable CRISPR-spacer integration reporter plasmids

A spacer could compensate for any steric hindrance effect on recruiting the transcriptional machinery at the promoter of the next module in the assembly line; such an effect could be induced by the supercoiling that results when the transcription of the previous module is taking place. However, there is no direct evidence that this may cause a problem, and therefore the argument in favor of using a spacer remains speculative.