Figure 1

Putative secondary structure of rDNA group I introns in Synechococcus. The group I introns are inserted after positions L1917, L1931, and L2593 of the large subunit ribosomal RNA gene. Open reading frames (ORFs) that encode putative homing endonucleases (HEs) with a single copy of the LAGLIDADG motif are inserted into peripheral regions. Paired elements (P1–P10) and every 10th nucleotide position in the introns are indicated on the structures. The L1931 and L2593 introns shown are from S. lividus strain C1, whereas the L1917 intron is from Synechococcus sp. C9.