Many of the gene products involved in DNA synthesis were initially defined by studying mutant E. coli strains that could not synthesize DNA. The dnaE gene encodes the α subunit of DNA polymerase III. What effect is expected from a mutation in this gene? How could the mutant strain be maintained?

Key Concepts

DNA Polymerase III

DNA Polymerase III is a crucial enzyme in prokaryotic DNA replication, responsible for synthesizing new DNA strands by adding nucleotides to a growing chain. It is a multi-subunit enzyme, with the α subunit encoded by the dnaE gene, which plays a key role in the polymerization process. Mutations in this gene can lead to defective DNA synthesis, impacting cell division and overall bacterial viability.

Mutant Strains

Mutant strains are organisms that have undergone genetic changes, resulting in altered phenotypes or functions. In the context of E. coli, studying these strains helps identify essential genes and their roles in cellular processes, such as DNA replication. By analyzing how these mutants behave under various conditions, researchers can infer the functions of specific genes and the consequences of their mutations.

Maintaining Mutant Strains

Maintaining mutant strains, particularly those with defects in essential genes like dnaE, often requires specific growth conditions that compensate for their deficiencies. For example, these strains may need to be cultured in media supplemented with nucleotides or other precursors to DNA synthesis, allowing them to survive despite their inability to replicate DNA effectively. This approach enables researchers to study the mutants without the immediate lethality of their genetic defects.