Redox-Responsive Zinc Finger Fidelity Switch in Homing Endonuclease and Intron Promiscuity in Oxidative Stress

• Published in: Current biology Vol. 21; no. 3; pp. 243 - 248
• Main Authors: Robbins, Justin B., Smith, Dorie, Belfort, Marlene
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 08.02.2011
• Subjects: active sites; Bacteriophage T4 - enzymology; Bacteriophage T4 - genetics; bacteriophages; Base Sequence; Binding Sites; cysteine; DNA; Endodeoxyribonucleases - chemistry; Endodeoxyribonucleases - genetics; Endodeoxyribonucleases - physiology; Gene Expression Regulation, Viral; Introns; Molecular Sequence Data; nucleotides; Oxidation-Reduction; Oxidative Stress; Phage T4; Sequence Analysis, DNA; Zinc - metabolism; zinc finger motif; Zinc Fingers - genetics
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2011.01.008

It is well understood how mobile introns home to allelic sites, but how they are stimulated to transpose to ectopic locations on an evolutionary timescale is unclear [1]. Here we show that a group I intron can move to degenerate sites under oxidizing conditions. The phage T4 td intron endonuclease, I-TevI, is responsible for this infidelity. We demonstrate that I-TevI, which promotes mobility and is subject to autorepression [2] and translational control [3], is also regulated posttranslationally by a redox mechanism. Redox regulation is exercised by a zinc finger (ZF) in a linker that connects the catalytic domain of I-TevI to the DNA binding domain. Four cysteines coordinate Zn2+ in the ZF, which ensures that I-TevI cleaves its DNA substrate at a fixed distance, 23–25 nucleotides upstream of the intron insertion site [4]. We show that the fidelity of I-TevI cleavage is controlled by redox-responsive Zn2+ cycling. When the ZF is mutated, or after exposure of the wild-type I-TevI to H2O2, intron homing to degenerate sites is increased, likely because of indiscriminate DNA cleavage. These results suggest a mechanism for rapid intron dispersal, joining recent descriptions of the activation of biomolecular processes by oxidative stress through cysteine chemistry [5, 6]. ► Zn2+ content of I-TevI intron endonuclease is redox sensitive ► Cleavage fidelity of I-TevI is lost upon ablation of the zinc finger ► Intron mobility to degenerate sites is increased when zinc finger is dysfunctional ► Oxidative stress stimulates intron promiscuity