 Such proteins were AcrF1, AcrF2, AcrF3, AcrF4 and AcrF5.Research found none of these proteins disrupted the expression of Cas genes nor the assembling of CRISPR molecules, so it was thought that those type I-F proteins directly affected the CRISPR–Cas interference.Further investigation confirmed this hypothesis with the discovery of 4 other proteins (AcrE1, AcrE2, AcrE3 and AcrE4), which were shown to impede "Pseudomonas aeruginosa"’s CRISPR-Cas system.