The Krüppel associated box (KRAB) domain is a category of transcriptional repression domains present in approximately 400 human zinc finger protein-based transcription factors (KRAB zinc finger proteins).

KRAB domains can be fused with dCas9 CRISPR tools to form even stronger repressors.

[11] The KRAB domain presents one of the strongest repressors in the human genome.

Ancestral KRAB A domains present in human PDRM9 proteins are even evolutionary conserved in mussel genomes.

Modern KRAB A domain sequences are found in coelacanth latimeria chalumnae and in Lungfish genomes.