Self-splicing group I and group II introns encode homologous (putative) DNA endonucleases of a new family
✍ Scribed by Alexander E. Gorbalenya
- Publisher
- Cold Spring Harbor Laboratory Press
- Year
- 1994
- Tongue
- English
- Weight
- 444 KB
- Volume
- 3
- Category
- Article
- ISSN
- 0961-8368
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✦ Synopsis
Abstract
A new family of protein domains consisting of 50–80 amino acid residues is described. It is composed of nearly 40 members, including domains encoded by plastid and phage group I introns; mitochondrial, plastid, and bacterial group II introns; eubacterial genomes and plasmids; and phages. The name “EX~1~H‐HX~3~H” was coined for both domain and family. It is based on 2 most prominent amino acid sequence motifs, each encompassing a pair of highly conserved histidine residues in a specific arrangement: EX~1~HH and HX~3~H. The “His” motifs often alternate with amino‐ and carboxy‐terminal motifs of a new type of Zn‐finger‐like structure CX~2, 4~CX~29–54~[CH]X~2, 3~[CH]. The EX~1~HH‐HX~3~H domain in eubacterial E2‐type bacteriocins and in phage RB3 (wild variant of phage T4) product of the nrdB group I intron was reported to be essential for DNA endonuclease activity of these proteins. In other proteins, the EX~1~HH‐EX~3~H domain is hypothesized to possess DNase activity as well. Presumably, this activity promotes movement (rearrangement) of group I and group II introns encoding the EX~1~HH‐HX~3~H domain and other gene targets. In the case of Escherichia coli restrictase McrA and possibly several related proteins, it appears to mediate the restriction of alien DNA molecules.