Overlap of the I-TevI ORF with core td intron sequence. (a) Secondary structure of the relevant portion of the td intron from phage T4 , labeled as in Figure 1. The I-TevI ORF is located in the P6 loop (solid blue line), but extends into the core td structure, as indicated by the last 20 nucleotides (colored red) of the I-TevI ORF, which contribute to P6a and P7. Short red lines to the side of these nucleotides indicate codons corresponding to the five carboxy-terminal amino acids of I-TevI (F241 to A245). The RNA hairpin that sequesters the I-TevI ribosome-binding site (RBS) is indicated in the P6 loop [55,59]. (b) Co-crystal structure of the I-TevI 130C DNA-binding domain with intronless DNA substrate , modified from PDB 1T2T using PyMol. The amino acids corresponding to the region of overlap with the td intron sequence are shown as red sticks, with the remainder of the I-TevI protein colored blue. The DNA strand backbones are in yellow with the bases in green. Note that the carboxy-terminal alanine (A245) was not present in the I-TevI structure. The zinc ion coordinated by the I-TevI zinc finger is shown as a blue sphere.
Edgell et al. BMC Biology 2011 9:22 doi:10.1186/1741-7007-9-22