| Upon infection of Escherichia coli, the bacteriophage T7 annexes the host protein thioredoxin to serve as a processivity factor for its DNA polymerase, T7 gene 5 protein. A genetic method was developed and used to probe the interactions between T7 DNA polymerase and E. coli thioredoxin. The strategy is to use E. coli thioredoxin mutant strains that are unable to support the growth of wild-type T7 to select for suppressor T7 strains containing mutations in gene 5 which compensate for the thioredoxin defect. Specifically, an E. coli strain harboring a glycine-74 to aspartate-74 (G74D) thioredoxin mutation does not support the growth of wild-type T7 phage, and six different mutations within T7 gene 5 could suppress this G74D thioredoxin defect. Each suppressor mutation alone is both necessary and sufficient to confer the suppressor phenotype. Three of the suppressor mutations (valine-3 to isoleucine, valine-32 to alanine, and alanine-45 to threonine) are located within the putative 3... |
