The reason for the low activity of Cas proteins in eukaryotes is not fully understood, but there are several factors that may contribute to this phenomenon. One possible reason is the difference in the structure of the chromatin between prokaryotes and eukaryotes. Chromatin is the complex of DNA and proteins that makes up the chromosomes, and it can inhibit the access of Cas proteins to the DNA target. Eukaryotic chromatin is more complex than prokaryotic chromatin and is tightly packaged with histone proteins, making it difficult for the Cas proteins to access their target DNA [4]. Additionally, eukaryotic DNA is methylated, which can further reduce the accessibility of Cas proteins to the target site.

Another possible reason for the low activity of Cas proteins in eukaryotes is the difference in the ribosomes between the two types of organisms. Ribosomes are the cellular machinery responsible for protein synthesis, and they differ in size and structure between prokaryotes and eukaryotes. Eukaryotic ribosomes are larger and more complex than prokaryotic ribosomes and may not efficiently translate Cas proteins.