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Self‐splicing group I and group II introns encode homologous (putative) DNA endonucleases of a new family

1994; Wiley; Volume: 3; Issue: 7 Linguagem: Inglês

10.1002/pro.5560030716

1469-896X

Alexander E. Gorbalenya,

Bacterial Genetics and Biotechnology

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.