A class of temperature sensitive E. coli mutants defective in DNA replication were identified that ceased replication immediately upon increase in…
A class of temperature sensitive E. coli mutants defective in DNA replication were identified that ceased replication immediately upon increase in temperature. Which of the following processes are likely to be defective in these mutants?
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Correct Answer: Option D
Explanation
Temperature-sensitive (ts) DNA replication mutants in E. coli that IMMEDIATELY stop replication upon shift to restrictive temperature must be defective in a process that is CONTINUOUSLY occurring at the replication fork during the elongation phase. Initiation is an episodic (once per cell cycle) event — ts initiation mutants would complete already-initiated rounds but not start new ones (delayed phenotype). Termination is also a discrete, episodic event at the end of replication — ts termination mutants would complete elongation but fail to terminate. Segregation occurs after replication is complete. Only elongation requires continuous enzymatic activity (DNA Pol III holoenzyme, helicase, primase on lagging strand) — so an instantaneous stop implies a ts defect in an elongation component such as the DNA Pol III,, orsubunits.