Conditional lethal mutants have proven indispensible in genetic and biochemical analyses of complex processes such as DNA replication. Temperature-sensitive (ts) mutations, which are one form of conditional lethal mutation, allow growth at one temperature (for example, 30oC) but not at a higher temperature (for example, 42oC). A large number of ts mutants have been isolated in E. coli. These mutant bacteria are defective in DNA replication at 42oC but not at 30oC. If the temperature of the medium is raised from 30oC to 42oC, these mutants stop making DNA in one of two characteristic ways. The 'quick stop' mutants halt DNA synthesis immediately, whereas the 'slow stop' mutants stop DNA synthesis only after a few minutes. Which of the following mutant proteins would you predict would display a 'quick stop' phenotype?
a. DNA topoisomerase I, a replication initiator protein, DNA ligase, and DNA helicase
b. DNA topoisomerase I, single-stranded DNA-binding protein, DNA ligase, and DNA helicase
c. DNA topoisomerase I, single-stranded DNA-binding protein, DNA primase, and DNA helicase
d. A replication initiator protein, single-stranded DNA-binding protein, DNA ligase, and DNA helicase
e. DNA topoisomerase I, single-stranded DNA-binding protein, DNA ligase, and DNA helicase
Conditional lethal mutants have proven indispensible in genetic and biochemical analyses of complex processes such as DNA replication. Temperature-sensitive (ts) mutations, which are one form of conditional lethal mutation, allow growth at one temperature (for example, 30oC) but not at a higher temperature (for example, 42oC). A large number of ts mutants have been isolated in E. coli. These mutant bacteria are defective in DNA replication at 42oC but not at 30oC. If the temperature of the medium is raised from 30oC to 42oC, these mutants stop making DNA in one of two characteristic ways. The 'quick stop' mutants halt DNA synthesis immediately, whereas the 'slow stop' mutants stop DNA synthesis only after a few minutes. Which of the following mutant proteins would you predict would display a 'quick stop' phenotype?
a. DNA topoisomerase I, a replication initiator protein, DNA ligase, and DNA helicase
b. DNA topoisomerase I, single-stranded DNA-binding protein, DNA ligase, and DNA helicase
c. DNA topoisomerase I, single-stranded DNA-binding protein, DNA primase, and DNA helicase
d. A replication initiator protein, single-stranded DNA-binding protein, DNA ligase, and DNA helicase
e. DNA topoisomerase I, single-stranded DNA-binding protein, DNA ligase, and DNA helicase
