Several temperature-sensitive mutant strains of E. coli display the following characteristics. Predict what enzyme or function is being affected by each mutation.
Okazaki fragments accumulate, and DNA synthesis is never completed.

Verified step by step guidance

1. Understand the biological context: Okazaki fragments are short DNA sequences synthesized on the lagging strand during DNA replication. Normally, these fragments are joined together to form a continuous strand.
2. Identify the process involved: The joining of Okazaki fragments requires the removal of RNA primers and the sealing of gaps between fragments. This involves enzymes such as DNA polymerase I and DNA ligase.
3. Consider the effect of mutation: If Okazaki fragments accumulate and DNA synthesis is never completed, it suggests a failure in either removing RNA primers or sealing the fragments together.
4. Focus on the key enzymes: DNA polymerase I removes RNA primers and fills in the gaps with DNA, while DNA ligase seals the nicks between Okazaki fragments to create a continuous strand.
5. Predict the affected enzyme or function: The mutation likely affects either DNA polymerase I's exonuclease activity (removal of RNA primers) or DNA ligase's ability to join fragments, preventing completion of lagging strand synthesis.

Key Concepts

Okazaki Fragments and Lagging Strand Synthesis

Okazaki fragments are short DNA segments synthesized discontinuously on the lagging strand during DNA replication. Their proper joining is essential for continuous DNA synthesis. Accumulation of these fragments indicates a defect in processing or joining steps of lagging strand replication.

Role of DNA Ligase

DNA ligase is the enzyme responsible for sealing nicks between Okazaki fragments by forming phosphodiester bonds. If DNA ligase is defective or inactive, Okazaki fragments accumulate because they cannot be joined into a continuous strand, halting DNA synthesis completion.

Temperature-Sensitive Mutations

Temperature-sensitive mutations produce proteins that function normally at permissive temperatures but lose activity at restrictive (higher) temperatures. Studying these mutants helps identify essential enzymes by observing which functions fail when the protein is inactivated.