Figure 2.

Secondary structure of the group I self-splicing intron in B. thuringiensis ssp. pakistani and ssp. colmeri nrdF. Predicted secondary structure of the nrdF intron. Small letters indicate coding sequence of the nrdF gene. Capital letters indicate intronic sequence. Bold capital letters indicate the ORF in the intron with the numbers in the loop in P6.1 representing the sequence of B. thuringiensis ssp. colmeri and ssp. pakistani, respectively. Conserved sequence elements (R and S), conserved base-paired regions (P1 to P9) and additional pairings (P6a, P7.1, P7.2, P9a, P9.1 and P9.2) are shown. Alignment between the 5′ and 3′ splice site can be promoted by the boxed nucleotides, UUAU, in the P1 loop and the AUGA, in exon 2, making pairing P10. Circled letters indicate differences from the other IVS6-containing strains.