Braun C J, Siedow J N, Williams M E, Levings C S
Department of Genetics, North Carolina State University, Raleigh 27695-7614.
Proc Natl Acad Sci U S A. 1989 Jun;86(12):4435-9. doi: 10.1073/pnas.86.12.4435.
URF13, the product of the mitochondrial T-urf13 gene, confers on Texas cytoplasmic male-steril maize (Zea mays L.) a unique susceptibility to a fungal pathogen (Bipolaris maydis race T) and sensitivity to its pathotoxin. Expression of URF13 in Escherichia coli imparts pathotoxin sensitivity to the bacterium. We show by ion uptake studies in E. coli that a pathotoxin-URF13 interaction causes membrane permeability. Similarly, mitochondrial dysfunction caused by membrane permeabilization probably accounts for increased colonization of maize carrying the Texas cytoplasm by toxin-producing pathogens. Site-directed mutagenesis studies show that approximately one-quarter of the amino acids at the carboxyl end of URF13 can be eliminated without affecting toxin sensitivity. We have identified two dicyclohexylcarbodiimide (DCCD) binding sites in the URF13 protein and show that one of the sites is involved in conferring DCCD protection against the pathotoxin. Substitutional mutations at this DCCD binding site also eliminate toxin sensitivity.
URF13是线粒体T-urf13基因的产物，它使德克萨斯细胞质雄性不育玉米（Zea mays L.）对一种真菌病原体（小斑病菌T小种）具有独特的易感性，并对其致病毒素敏感。URF13在大肠杆菌中的表达赋予该细菌对致病毒素的敏感性。我们通过在大肠杆菌中的离子摄取研究表明，致病毒素与URF13的相互作用导致膜通透性增加。同样，由膜通透性引起的线粒体功能障碍可能是携带德克萨斯细胞质的玉米被产毒素病原体侵染增加的原因。定点诱变研究表明，URF13羧基末端约四分之一的氨基酸可以被去除而不影响对毒素的敏感性。我们在URF13蛋白中鉴定出两个二环己基碳二亚胺（DCCD）结合位点，并表明其中一个位点参与赋予DCCD对致病毒素的保护作用。该DCCD结合位点的替代突变也消除了对毒素的敏感性。
