Alternative splicing of a group II intron in a surface layer protein gene in Clostridium tetani.
Group II introns are ribozymes and retroelements found in bacteria, and are thought to have been the ancestors of nuclear pre-mRNA introns. Whereas nuclear introns undergo prolific alternative splicing in some species, group II introns are not known to carry out equivalent reactions. Here we report a group II intron in the human pathogen Clostridium tetani, which undergoes four alternative splicing reactions in vivo. Together with unspliced transcript, five mRNAs are produced, each encoding a distinct surface layer protein isoform. Correct fusion of exon reading frames requires a shifted 5' splice site located 8 nt upstream of the canonical boundary motif. The shifted junction is accomplished by an altered IBS1-EBS1 pairing between the intron and 5' exon. Growth of C. tetani under a variety of conditions did not result in large changes in alternative splicing levels, raising the possibility that alternative splicing is constitutive. This work demonstrates a novel type of gene organization and regulation in bacteria, and provides an additional parallel between group II and nuclear pre-mRNA introns.
Department of Biological Sciences, University of Calgary, 2500 University Dr. NW, Calgary, Alberta T2N 1N4, Canada.
Bonnie A
BA
McNeil
Dawn M
DM
Simon
Steven
S
Zimmerly
D017398:Alternative Splicing; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D003017:Clostridium tetani / Q000235:genetics*; D005798:Genes, Bacterial; D007438:Introns; D008562:Membrane Glycoproteins / Q000235:genetics*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D022821:RNA Splice Sites; D016337:RNA, Catalytic / Q000737:chemistry* / Q000378:metabolism
D001426:Bacterial Proteins; D008562:Membrane Glycoproteins; D022821:RNA Splice Sites; D016337:RNA, Catalytic; C055764:S-layer proteins