# Bacterial Recombinational DNA Repair ## The RecBCD Pathway While the main purpose of the RecBCD pathway is to facilitate DNA repair, it can also be used to store extracellular DNA. | Enzyme/Protein | Functional Form | Function | | -------------- | --------------- | ------------------------------------------ | | RecA | | Bacterial recombinase | | RecB | | 3’→5’ helicase, forms 3’ strand extensions | | RecC | | Binds chi site, forms 3’ strand extensions | | RecD | | 5’→3’ helicase, forms 3’ strand extensions | (Rec stands for “recombination”) | Enzyme/Protein | Functional Form | Function | | -------------- | --------------- | -------- | | RecF | | | | RecO | | | | RecR | | | - **RecA** is the primary recombinase enzyme in bacteria - Loaded by *RecBCD* for double-strand breaks - Loaded by *RecFOR* for DNA gaps ![[Pasted image 20250128015146.png]] ![[Pasted image 20250128032736.png|325]] --- | Protein | Description | | ------- | -------------------------------------------------------------------------------------------------------- | | RecB | A type of helicase;<br>facilitates recA loading<br>non-specific nuclease<br>part of RecBCD | | RuvC | Resolves the Holliday junction at (A/T)TT(G/C) site (sequence specific)<br><br>(*U*nder in*V*estigation) | | RuvAB | DNA translocase to move DNA (from A → B) | | Spo11 | Eukaryotes | - recA in prokaryotes is analagous to the single stranded binding (SSB) proteins found in eukaryotes - Chi sites help degradation of one strand and *slow down* the degradation of another. - Double stranded DNA breaks are only ever intentional within eukaryotes, not prokaryotes - Often done to increase genetic diversity during recombination - Always consider what auxilary proteins will be present on DNA (ssDNA & dsDNA) - ssDNA can’t be left alone in eukaryotes - The Holliday junction can only be cleaved two ways (vertically or horizontally, never in an L shape) - The rate limiting step for a lot of biological activity is the initialization step - i.e. loading of RecA by RecBCD protein begins slowly, but increases in speed during the extension phase.