Catalytic GIY-YIG domain of putative intron-encoded endonuclease bI1 and similar proteins
The prototype of this family is a putative intron-encoded mitochondrial DNA endonuclease bI1 found in mitochondrion Ustilago maydis. This protein may arise from proteolytic cleavage of an in-frame translation of COB exon 1 plus intron 1, containing the bI1 open reading frame. It contains an N-terminal truncated non-functional cytochrome b region and a C-terminal intron-encoded endonuclease bI1 region. The bI1 region shows high sequence similarity to endonucleases of group I introns of fungi and phage and might be involved in intron homing. Many uncharacterized bI1 homologs existing in fungi and chlorophyta in this family do not contain the cytochrome b region, but have a standalone bI1-like region, which contains a GIY-YIG domain and a minor-groove binding alpha-helix nuclease-associated modular domain (NUMOD). This family also includes a Yarrowia lipolytica mobile group-II intron COX1-i1, also called intron alpha, encoding protein with reverse transcriptase activity. The group-II intron COX1-i1 may be involv ed both in the generation of the circular multimeric DNA molecules (senDNA alpha) which amplify during the senescence syndrome and in the generation of the site-specific deletion which accumulates in the premature-death syndrome.
Jiyao W et al.(2023). "The conserved domain database in 2023.",