A strain of E. coli is identified as having a null mutation of the RecA gene. What biological property do you expect to be absent in the mutant strain? What is the molecular basis for the missing property?

Verified step by step guidance

1. Understand the role of the RecA gene: The RecA protein is essential for homologous recombination and DNA repair in E. coli. It facilitates the exchange of genetic material between homologous DNA sequences and is involved in the SOS response to DNA damage.
2. Identify the biological property affected: A null mutation in the RecA gene means the RecA protein is non-functional or absent. This would result in the inability of the mutant strain to perform homologous recombination and repair DNA damage effectively.
3. Explain the molecular basis: RecA binds to single-stranded DNA (ssDNA) and forms a nucleoprotein filament. This filament searches for homologous sequences in double-stranded DNA (dsDNA) and facilitates strand exchange, a critical step in DNA repair and recombination. Without RecA, this process cannot occur.
4. Discuss the consequences of the mutation: The mutant strain would be highly sensitive to DNA-damaging agents (e.g., UV radiation or chemical mutagens) because it cannot repair DNA damage efficiently. Additionally, the SOS response, which is triggered by extensive DNA damage, would be impaired as RecA is required to activate the LexA repressor cleavage.
5. Summarize the missing property: The absence of RecA results in the loss of homologous recombination and an impaired ability to repair DNA damage, leading to genomic instability and increased sensitivity to environmental stressors.

Key Concepts

RecA Protein Function

RecA is a crucial protein in bacteria that facilitates homologous recombination and DNA repair. It plays a key role in the SOS response, allowing cells to repair damaged DNA and maintain genomic integrity. A null mutation in the RecA gene results in the absence of this protein, impairing the cell's ability to effectively respond to DNA damage.

Homologous Recombination

Homologous recombination is a process by which genetic material is exchanged between similar or identical DNA molecules. This mechanism is essential for repairing double-strand breaks in DNA and for genetic diversity during meiosis. In the absence of RecA, the mutant E. coli strain would be unable to perform homologous recombination, leading to increased susceptibility to DNA damage.

SOS Response

The SOS response is a global response to DNA damage in bacteria, activating a set of genes involved in DNA repair and mutagenesis. RecA protein is central to this response, as it helps to initiate the repair processes. Without RecA, the mutant strain would lack the ability to mount an effective SOS response, resulting in an inability to repair DNA damage and increased cell death.