HUH-tag

HUH endonucleases (HUH-tags) are sequence-specific single-stranded DNA (ssDNA) binding proteins originating from numerous species of bacteria and viruses.

Some DNA viruses code for an HUH endonuclease which initiates rolling circle replication of the viral genome, and this process defines the realm Monodnaviria.

[2] HUH endonucleases generally have two histidine (H) residues in the active site coordinating a metal cation (Mg2+ or Mn2+) that interacts with the phosphate backbone of DNA.

These residues allow for a nucleophilic attack, most commonly by an activated tyrosine of the scissile phosphate in the DNA backbone, generating a 5' covalent bond with the ssDNA.

In contrast to other DNA-protein linkage approaches, this reaction occurs at ambient conditions and does not require any additional modifications.

Generic HUH endonuclease binding to single-stranded DNA.
WDV Rep reaction mechanism of nucleophilic attack on the DNA backbone.