Answer to Question #251032 in Microbiology for Francois

Question #251032

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);   (2) a strain without RNaseH proteins; 

Expert's answer
  1. This strain is not able to replicate the proper DNA molecule because after deleting the primer it is no longer proceeds the formation of DNA instead. In such situation, descendent DNA would have gaps, where RNA-primers were.
  2. This strain is able to produce adequate DNA molecules during the process of replication. Without RNaseH, all of the primers would be proceed by Pol 1 and needed DNA would be obtained.

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