Fig. 2

The [D1,2] stwintron of the putative lipase encoding gene of A. niger ATCC 1015. a Depicts the determined A. niger lipS intron–exon structure with the exact sizes of the exons and intervening sequences given: The stwintron is the second intervening sequence. b Schematically the structure of the stwintron that splits the CCU codon of Pro184, and the two consecutive splicing events necessary to remove it. Exonic sequences (in capitals) are grouped as the consecutive codons (Val181–Phe182–Ala183–Pro184–Lys185–Tyr186–Arg187). The internal intron is marked by the lighter grey bar; its 5′-donor-, lariat branch point domain- and 3′-acceptor sequences are printed in blue lettering. The external intron is marked by the darker grey bar; its 5′-donor-, lariat branch point domain- and 3′-acceptor sequences are printed in red lettering. c The existence of the splicing intermediate from which the internal intron has been removed by the first excision, has been confirmed experimentally (GenBank MF612153). The newly formed donor splice site sequence of the retained external intron, (5′-gugagu), is underlined