Unconventional GIY-YIG homing endonuclease encoded in group I introns in closely related strains of the Bacillus cereus group.
Several group I introns have been previously found in strains of the Bacillus cereus group at three different insertion sites in the nrdE gene of the essential nrdIEF operon coding for ribonucleotide reductase. Here, we identify an uncharacterized group IA intron in the nrdF gene in 12 strains of the B. cereus group and show that the pre-mRNA is efficiently spliced. The Bacillus thuringiensis ssp. pakistani nrdF intron encodes a homing endonuclease, denoted I-BthII, with an unconventional GIY-(X)8-YIG motif that cleaves an intronless nrdF gene 7 nt upstream of the intron insertion site, producing 2-nt 3' extensions. We also found four additional occurrences of two of the previously reported group I introns in the nrdE gene of 25 sequenced B. thuringiensis and one B. cereus strains, and one non-annotated group I intron at a fourth nrdE insertion site in the B. thuringiensis ssp. Al Hakam sequenced genome. Two strains contain introns in both the nrdE and the nrdF genes. Phylogenetic studies of the nrdIEF operon from 39 strains of the B. cereus group suggest several events of horizontal gene transfer for two of the introns found in this operon.
Nord
David
D
Department of Molecular Biology and Functional Genomics, Stockholm University, SE-10691 Stockholm, Sweden.
Sjöberg
Britt-Marie
BM
D000595:Amino Acid Sequence; D001409:Bacillus cereus / Q000145:classification; D001413:Bacillus thuringiensis / Q000145:classification / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D004706:Endodeoxyribonucleases / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D007438:Introns; D008969:Molecular Sequence Data; D009876:Operon; D010802:Phylogeny; D012326:RNA Splicing; D012329:RNA, Bacterial / Q000737:chemistry; D012264:Ribonucleotide Reductases / Q000235:genetics*; D016415:Sequence Alignment
D001426:Bacterial Proteins; D012329:RNA, Bacterial; C114872:NrdF protein, bacteria; D012264:Ribonucleotide Reductases; D004706:Endodeoxyribonucleases