Effector involved in the disease saprolegniosis in salmonids and other freshwater fish, resulting in considerable economic losses in aquaculture (PubMed:29904064). Within the host fish cells, Htp3 is released from vesicles into host cytosol where it degrades nucleic acids (PubMed:29904064). The nuclease activity shows a general salt dependency with a clear reduction by magnesium and sulfate ions. Interacts with the host cell surface endoplasmin gp96, in order to get translocated into to host cell (PubMed:29904064). Interacts with the effector Htp1, in order to get released from vesicles into the host cytosol (PubMed:29904064). Uptake into host cells is more efficient at a lower pH of 5.5. S.parasitica acidifies the pH of its environment, which likely leads to the exposure of a gp96 protein to the host cell surface. The gp96 protein is working as a receptor and mediates the translocation of Htp3 via lipid rafts into the cell. Finally, Htp3 is released from vesicles with the help of other effector proteins, such as Htp1, into the cytosol where it is functionally active as a nuclease. The conserved RxLR motif does not seem to be involved in self-translocation into fish cells. The C-terminus (residues 200 to 211) is predicted to form a short helix with charged amino acids and is required for the self-translocation into fish cells. In the N-terminal section; belongs to the RxLR effector family. In the C-terminal section; belongs to the LCL3 family.