Nuclear localization sequence is an amino acid sequence that contains signals for a protein to be imported into the nucleus. The signal is typically made of a one or more positively charged amino acids lysine or arginine. The signal is essential for certain eukaryotic proteins to cross the nuclear membrane and enter the nucleus. These proteins essentially have their function in the nucleus.
Since prokaryotes lack a nucleus and nuclear membrane, there is no need for nuclear localization signals on their proteins. Hence, the signals are absent in their polymerases. However, eukaryotes contain a nuclear membrane that encloses the genetic material. The polymerases that aid in replication and transcription of genetic material must cross the nuclear membrane, since they are synthesized in the cytoplasm. Therefore, eukaryotic DNA and RNA (Deoxyribo nucleic acid and Ribonucleic acid) polymerases contain nucleotide localization sequences.