At the 4-cell stage, the EMS cell requires a signal from its neighbor (and sister cell), the P2 blastomere.

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#Unit 3. Fundamental Processes

dat locus is regulatory

In particular, a locus called dat has a large concentration of DnaA-binding sites. It binds about 80 more DnaA molecules than the origin.

Deletion of dat causes initiation to occur more frequently. This significantly increases the amount of DnaA available to the origin.

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DnaA promotes replication

SeqA delays new round of replication by inhibiting dam methylase binding

Dam methylase provide substrate for DnaA

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#Unit 3. Fundamental Processes

DnaA mutants make replication asynchronous

SeqA mutant cells don’t delay rereplication for 13 minutes

Dam methylase mutants stops rereplication

SeqA-/dam+ accumulation of methylated products

SeqA+/dam- accumulation of hemimethylated products

SeqA-/dam- accumulation of hemimethylated products

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#Unit 3. Fundamental Processes

There are two basic types of DNA synthesis

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#Unit 3. Fundamental Processes

Semiconservative replication

DNA repair reaction

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#Unit 3. Fundamental Processes

All prokaryotic and eukaryotic DNA polymerases share the same fundamental type of synthetic activity -an antiparallel synthesis from 5’ to 3’ from a template that is 3’ to 5’. This means adding nucleotides one at a time to a 3’–OH end.