Protein single-stranded regions

At the growth fork it is necessary that the parental double helix be unwound to present further single-stranded regions to serve as templates for continued replication. The dnaB protein of E. coli is believed to be a helicase that directly catalyzes this process. 

The CCA terminus containing the amino acid attachment site extends from one end of the L. This single-stranded region can change conformation during amino acid activation and protein synthesis. 

Figure 30.30 The signal-recognition particle. The signal-recognition particle (SRP) consists of six proteins (one of which is SRPS-I) and one 300-nucleotide R,NA molecule. The RNA has a complex structure with many double-hclicat stretches punctuated by single-stranded regions, shown as circles. [After H, Lodish et al., Molecular Cell Biology, 5th ed.

DNA gyrase introduces a swivel point in advance of the movement of the replication fork. A helix-destabilizing protein, a helicase, binds at the replication fork and promotes unwinding. The exposed single-stranded regions of the template DNA are stabilized by a DNA-binding protein. 

Besides the DNA polymerases themselves, many other proteins are involved in replication. DNA gyrase induces negative supercoils in the DNA to compensate for the positive supercoils that would form because of strand separation, and helicase induces strand separation. Single-stranded binding proteins protect the single-stranded regions from nucleases. 

How is single-stranded DNA protected long enough for replication Specific proteins called singlestrand binding proteins hind to the single-stranded regions and protect them from nucleases. 

---