Answer to Question #250690 in Microbiology for Hloni

Question

DNA polymerase I (Pol I) of E. coli consists of three functional parts (domains): an N-terminal domain with 5 ´ to 3 ´ exonuclease activities required for removal of the RNA primer, a central domain responsible for 3 ´ to 5 ´ exonuclease proofreading, and a C-terminal domain with polymerase activity. Pol I is thought to simultaneously remove RNA primers and fill in the gaps that result. A group of proteins known as RNaseH also have 5 ´ to 3 ´ exonuclease activity and can thus remove RNA primers. However, they lack the other two functions observed for Pol I. Predict the ability of the following mutants to replicate DNA:
(1) a strain with a mutant gene encoding Pol I such that it no longer has polymerase activity (but retains both types of nuclease activities); [3]
(2) a strain without RNaseH proteins;

Answer 1

RNA polymerase has

5' to 3' econuclease activity- primer removal

3' 5 ' exonuclease- for proof reading

Central domain- polymerization

This polymerization domain is essential for synthesis of DNA.

1) no replication of DNA- essential polymerase part is mutant

2) with out RNase H- polymerization occur DNA polymerse has all the activities required for replication