Cleaves both 3' and 5' ssDNA extremities of branched DNA structures. Binds to ssDNA. Activity is modulated by PCNA. PCNA increases the binding affinity of NucS towards ssDNA as well as branched DNA substrates carrying either 3' or 5' flaps. PCNA is also required for optimal loading of NucS on its substrates and to direct activity towards ss/dsDNA junction. Homodimer. Interacts with PCNA. Composed of two independent domains separated by a small linker. The N-terminal region contains the ssDNA binding site and the C-terminal region contains the nuclease active site. Belongs to the NucS endonuclease family.