Question

Suppose you are given a new temperature sensitive bacterial mutant that grows normally at 37 degrees c but cannot replicate its chromosomes properly at 42
c. to investigate the nature of the underlying defect, you incubate the cells at 42 c with radioactive substrates required for dna synthesis. after one hour you find that the cell population has doubled its dna content, suggesting that dna replication can still occur at 42
c. moreover, centrifugation reveals that all of this dna has the same large molecular weight as does the original dna present in the cells. when the dna is denatured, however, you discover that 75% of the resulting single stranded dna has a molecular weight that is half that of the original double-stranded dna, and the remaining 25% of the dna has a much lower molecular weight. based on the preceding results, what gene do you think is defective in these cells?

Answer 1

The DNA denaturation step in the experiment released the one full-length strands of the original DNA and the unjoined Okazaki fragments of the lagging strand.