Font Paragraph 2. You do a mutational analysis on Tar, the aspartate receptor of
ID: 148597 • Letter: F
Question
Font Paragraph 2. You do a mutational analysis on Tar, the aspartate receptor of E. coli, by making specific mutations of the Tar gene and transforming these forms into a bacterial strain such that homologous recombination inserts your version of the gene. b. (3) You start out with a series of different (not the one in part a) bp substitution (point) mutations in Tar that act as null alleles (in a mutant line lacking all other receptors). By screening for reversions, you identify not only bone fide reversions of your original Tar mutations, but also mutations in other genes as well (hint: think about intergenic suppression). Given what you know about bacterial chemotaxis, and the protein-protein interactions involved, what genes are these likely to be, and why?Explanation / Answer
Movement of an organism in response to chemical stimulus is called chemotaxis. Bacteria such as E.coli rotate into counter clock wise because of flagella into single rotating bundle causing the E.coli swim in to straight line while rotation in clockwise breaks the flagella bundle into apart and in different direction so bacteria tumble in place. Bacteria show chemotaxis behavior and moving in straight line after sensing a chemical gradients, however moving in wron direction it will tumble in place.
Methyl accepting chemotaxis protein (MCPs) is a transmembrane protein responsible for sensing chemical gradient in the bacteria. MCPs receptor may bind directally or indirectaly by interaction to periplasmic space protein. Signal produced by these receptor will transmitt across the plasma membrane and activate the che protein of cytosol and these che protein alter the tumbling frequency with altering receptors.
CheW and CheA protein involve in flagellum regulation. absense of the receptors results autophosphorylation of the Histidine kinase residue of CheA, CheA in turns transfer phosphoryl group to the aspartate residue in response regulator of CheY and CheB. This mechanism is called two component rregulatory system off bacteria. Tumbling is induced by CheY proteein after interaction with FliM protein, which turn counter clock wise to clock wise movement of bacterial flagellum.
CheB activated by CheA aact as a methyl esterase remove methylgroup from the glutamate on the cytosolic side of the receptor its work antagonistically with CheR a methyl transferase which add methyl groups to the glutamate
E.coli serine receptor Tsr block the wild typt Tar (aspartate receptor) function by making difective mixed trimers of dimer. An epistatic defect of Tsr with a wild type Tar show no chemotactic movement in bacteria in response to stimulus while mutant of Tar will restore cheemotactic response to stimulus by restoring Tsr serine receptor.