FEN-like PIN domains of Mkt1, a global regulator of mRNAs encoding mitochondrial proteins and eukaryotic homologs. The Mkt1 gene product interacts with the Poly(A)-binding protein associated factor, Pbp1, and is present at the 3' end of RNA transcripts during translation. The Mkt1-Pbp1 complex is involved in the post-transcriptional regulation of HO endonuclease expression. Mkt1 and eukaryotic homologs are atypical members of the structure-specific, 5' nuclease family (FEN-like). Canonical members of the FEN-like family possess a PIN domain with a two-helical structure insert (also known as the helical arch, helical clamp or I domain) of variable length (approximately 16 to 800 residues), and at the C-terminus of the PIN domain a H3TH (helix-3-turn-helix) domain, an atypical helix-hairpin-helix-2-like region. Both the H3TH domain (not included in this model) and the helical arch/clamp region are involved in DNA binding. Although Mkt1 appears to possess both a PIN and H3TH domain, the Mkt1 PIN domain lacks several of the active site residues necessary to bind essential divalent metal ion cofactors (Mg2+/Mn2+) required for nuclease activity in this family. Also, Mkt1 lacks the glycine-rich loop in the H3TH domain which is proposed to facilitate duplex DNA binding.