Vertebrates have three homologues of the Drosophila hedgehog gene: sonic hedgehog (shh), desert hedgehog

(dhh), and indian hedgehog (ihh)

TLS Online TPP Program

#Id: 3400

#Unit 3. Fundamental Processes

Cleavage of both LexA and UmuD is stimulated by a protein called RecA, which is activated by single-stranded DNA resulting from DNA damage.

TLS Online TPP Program

#Id: 3402

#Unit 3. Fundamental Processes

LexA repressor (Mr 22,700) inhibits transcription of all the SOS genes, and induction of the SOS response requires removal of LexA

TLS Online TPP Program

#Id: 3404

#Unit 3. Fundamental Processes

The LexA repressor is inactivated when it catalyzes its own cleavage at a specific Ala–Gly peptide bond.

TLS Online TPP Program

#Id: 3405

#Unit 3. Fundamental Processes

SOS response in E. coli: 

The LexA protein is the repressor in this system, which has an operator site near each gene. Because the RecA gene is not entirely repressed by the LexA repressor, the normal cell contains about 1,000 RecA monomers. 

TLS Online TPP Program

#Id: 3412

#Unit 3. Fundamental Processes

SOS response in E. coli:

When DNA is extensively damaged (such as by UV light), DNA replication is halted and the number of single-strand gaps in the DNA increases.

RecA protein binds to this damaged, single-stranded DNA, activating the protein’s co-protease activity.

While bound to DNA, the RecA protein facilitates cleavage and inactivation of the LexA repressor. When the repressor is inactivated, the SOS genes, including RecA, are induced;

TLS Online TPP Program

#Id: 3417

#Unit 3. Fundamental Processes

Alternative models for translesion synthesisIn; Two models explain the mechanism of translesion synthesis, each likely to be true under particular circumstances.

The polymerase-switching model,

The gap-filling model,