Fig. 7

Putative polypeptides encoded by the cox2-splitting DNA insert in the C. p. fossulana mitogenome. a Western blot and ribbon diagram of the I-TASSER-modeled three-dimensional structure of the QNU (the larger of its two isoforms) polypeptide. The tertiary structure was predicted by combining de novo and locally applied template-based modeling (PDB templates for local structure predictions were: 1wOrA, 3iymA, 2ocwA, 1pclA, 3cm9S). Signature motif and regions with similarity to nucleic acid-interacting proteins (Nai) and the active site of HNH homing endonucleases (HNH) are indicated on the polypeptide linear model. The inset shows the nuclease activity assay of the recombinant QNU using plasmid DNA as substrate, analyzed by agarose gel electrophoresis. No plasmid degradation was observed in the absence of recombinant proteins (P mock). The addition of rQNU caused a decrease in both SC and C forms of the plasmid and smearing of the L form, indicating at least endonuclease activity of the recombinant QNU (+rQNU). Addition of rΔQNU had no effect on the level of any form of the plasmid, indicating the absence of nuclease activity (+rΔQNU) over a 2-h incubation at 37 °C. Plasmid topology: SC, supercoil; L, linear; C, coil. Deletion of Gln-Asn (QN) repeats suppressed the nuclease activity of the rQNU polypeptide. b Western blot of the putative WFW polypeptide and deduced sequence of the repetitive signature motif of WFW that was predicted to adopt helical structure stabilized by Trp residues