The Ll.LtrB intron from Lactococcus lactis excises as circles in vivo: insights into the group II intron circularization pathway

RT-PCR amplification of excised intron junctions. (A) Schematic of the Ll.LtrB splicing pathway (branching). Position of the primers used to amplify the intron splice junction is depicted (open arrows, 287 bp). (B) RT-PCR amplifications performed on total RNA extracts from L. lactis (NZ9800ΔltrB) harboring different Ll.LtrB constructs expressed under the control of the P₂₃ constitutive promoter. (C) RT-PCR amplicons of excised introns (B) were phosphorylated and cloned in pBS (SmaI). Their sequences (Supplemental Table S1) correspond to lariats, circles, or alternatively circularized products (Alt. Cir.). Some of the intron junctions denoted by an asterisk have additional non-encoded nucleotides at the splice junction (Supplemental Table S1).