DNA polymerase I (Pol I) of E. coli consists of three functional parts (domains): an N-terminal domain with 59 to 39 exonuclease activity required for removal of the RNA primer, a central domain responsible for 39 to 59 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 (figure 13.14). A group of proteins known as RNaseH also have 59 to 39 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; (3) a strain with a mutant gene encoding Pol I such that it no longer has 59 to 39 exonuclease activity (but retains 39 to 59 nuclease and polymerase activities); (4) a strain with the mutant Pol I described in (3) and a strain lacking all RNaseH proteins. Explain your reasoning for each.
Gene Interactions
When the expression of a single trait is influenced by two or more different non-allelic genes, it is termed as genetic interaction. According to Mendel's law of inheritance, each gene functions in its own way and does not depend on the function of another gene, i.e., a single gene controls each of seven characteristics considered, but the complex contribution of many different genes determine many traits of an organism.
Gene Expression
Gene expression is a process by which the instructions present in deoxyribonucleic acid (DNA) are converted into useful molecules such as proteins, and functional messenger ribonucleic (mRNA) molecules in the case of non-protein-coding genes.
DNA polymerase I (Pol I) of E. coli consists of three functional parts (domains): an N-terminal domain with 59 to 39 exonuclease activity required for removal of the RNA primer, a central domain responsible for 39 to 59 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 (figure 13.14). A group of proteins known as RNaseH also have 59 to 39 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; (3) a strain with a mutant gene encoding Pol I such that it no longer has 59 to 39 exonuclease activity (but retains 39 to 59 nuclease and polymerase activities); (4) a strain with the mutant Pol I described in (3) and a strain lacking all RNaseH proteins. Explain your reasoning for each.
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