Question

E. coli DNA photolyase binds single or double-stranded DNA without regard to sequence, and has a cavity corresponding to a pyrimidine dimer. True or False?

DNA polymerase I (Pol I) makes contact with both the phosphate backbone and the bases of duplex DNA. True or False?

Answer 1

Answer 1 true It binds to UV-damaged DNA containing pyrimidine dimers and, upon absorbing a near-UV photon (300 to 500 nm), breaks the cyclobutane ring joining the two pyrimidines of the dimer.

2) false :

Pol I possesses four enzymatic activities:

1. A 5'?3' (forward) DNA-Dependent DNA polymerase activity, requiring a 3' primer site and a template strand
2. A 3'?5' (reverse) exonuclease activity that mediates proofreading
3. A 5'?3' (forward) exonuclease activity mediating nick translation during DNA repair.
4. A 5'?3' (forward) RNA-Dependent DNA polymerase activity. Pol I operates on RNA templates with considerably lower efficiency (0.1–0.4%) than it does DNA templates, and this activity is probably of only limited biological significance.^[