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H3TH domain 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. Conical members of this family possess a PIN (PilT N terminus) domain with a helical arch/clamp region/I domain (not included here) and inserted within the PIN domain is an atypical helix-hairpin-helix-2 (HhH2)-like region. This atypical HhH2 region, the H3TH (helix-3-turn-helix) domain, has an extended loop with at least three turns between the first two helices, and only three of the four helices appear to be conserved. 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. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",