TAL effector: Difference between revisions

'''Figure 2''': Domain organization of PthXo1 and structure of a single TAL effector repeat

TAL effectors contain N-terminal signals for bacterial type III secretion, tandem repeats that specify the target nucleotide sequence, nuclear localization signals, and a C-terminal region that is required for transcriptional activation. PthXo1 contains 23.5 canonical repeats (color coded to match Figure 2) that contact the DNA target found in the promoter of the rice Os8N3 gene (17). Blue bases correspond to positions in the target where the match between protein and DNA differs from the optimal match specified by the recognition code (3,4). Arrows indicate the start and end of the crystallized protein construct. In the structure, repeats 22 to 23.5 are poorly ordered, as are the C-termini of the two N-terminal cryptic repeats. The sequence and structure of a representative repeat (#14) is shown; RVD residues (HD) that recognize cytosine are red.<ref> PMID:22222791 </ref>

'''Figure 3''': All of the repeats in the DNA-bound PthXo1 structure form highly similar two-helix bundles (Figure 1c). The helices span positions 3 to 11 and 14 to 33, locating the RVD in a loop between them. A proline located at position 27, creates a kink in the second helix that appears to be critical for the sequential packing and association of tandem repeats with the DNA double helix. The packing of consecutive helices within and between individual repeats is left-handed, in contrast to the right-handed packing of helices found in TPR proteins (10). The modular architecture of the TAL effector repeats is reminiscent of the mitochondrial transcription terminator mTERF (11) and the RNA-binding attenuation protein TRAP (12);