The single group-I intron in the chloroplast rrnL gene of Chlamydomonas humicola encodes a site-specific DNA endonuclease (I-ChuI).
The single group-I intron (ChLSU.1) in the chloroplast (cp) large subunit rRNA-encoding gene (rrnL) of the green alga Chlamydomonas humicola is located at a position at which no introns have previously been characterized in other systems. In the present study, the nucleotide (nt) sequence of this 1118-bp intron was found to contain an internal open reading frame (ORF) that potentially encodes a basic protein of 218 amino acid residues. The putative C. humicola protein features two copies of the LAGLI-DADG motif and is part of the family of intron-encoded proteins comprising the endonucleases (ENases), I-SceI, I-SceIV and I-CsmI. Expression of the ChLSU.1 intron ORF in vitro in the presence of a 260-bp DNA fragment containing the exon 1-2 junction of an intronless version of the C. humicola rrnL resulted in specific cleavage of the DNA fragment very close to the intron insertion site. This novel intron-encoded ENase, designated I-ChuI, was also shown to generate a staggered cut with 4-nt (CTCG) 3'-OH overhangs 2 bp downstream from the intron insertion site.
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Département de biochimie, Faculté des sciences et de génie, Université Laval, Québec, Canada.
Mercier
J P
JP
Lemieux
C
C
Turmel
M
M
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002696:Chlamydomonas / Q000235:genetics*; D002736:Chloroplasts / Q000737:chemistry*; D004706:Endodeoxyribonucleases / Q000235:genetics*; D017343:Genes, Plant; D017125:Genes, Protozoan; D007438:Introns; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D016053:RNA, Protozoan / Q000235:genetics; D012335:RNA, Ribosomal / Q000235:genetics*; D016415:Sequence Alignment
D009838:Oligodeoxyribonucleotides; D016053:RNA, Protozoan; D012335:RNA, Ribosomal; D004706:Endodeoxyribonucleases