Colinearity of Gene Structure and its Polypeptide Product

Colinearity of Gene Structure and its Polypeptide Product

	Colinearity of Gene Structure and its Polypeptide Product - The gene is an unbranched structure consisting of a linear sequence of nucleotide pairs. The polypeptide chain is also unbranched and consists of a linear series of amino acid residues. A linear correspondence between a gene and the polypeptide chain synthesized by it was thus indicated. This was established by Yanofsky and his coworkers (1964) through a study of E. coli tryptophan synthetase. This enzyme consists of two chains, ex and p.
A genetic map of the ex chain gene was first prepared as follows. A series of mutant bacteria incapable of growing in the absence of tryptophan were isolated. The positions of mutations on the genetic map of the chain gene were determined by recombination studies with the transducing bacteriophage Plkc. These bacteriophages incorporate a portion of host DNA into their own DNA, and on infecting other bacteria may transfer some of the genetic material to the DNA of the second host through a recombination process. The complete amino acid sequence of the 268 residues of the ex chain of tryptophan synthetase was established.
The location of amino acid substitutions in the polypeptide chain for 10 mutations were then determined. It was found that the order of mutations on the genetic map corresponded with the order of amino acid substitutions in the α-polypeptide. It was thus concluded that the ex chain gene and its polypeptide product are colinear. Sarabhai et al (1964) arrived at the same conclusion by studying monsense mutations leading to premature chain termination during the synthesis of coat protein of the T4 bacteriophage.
Colinearity of the gene and its polypeptide product has been verified by studying RNA containing bacteriophages like f2, R17, MS2 and Qβ. The genetic information in these RNA viruses is contained in only three genes. The RNA molecule consists of only 3,500-4,000 nucleotides. By working out the nucleotide sequences of phage RNA molecules and the amino acid sequences of some of the proteins specified by the RNA, colinearity has been verified. (For exceptions to the colinearily principle see 'Split genes').

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Third Base Deciphering the Code Use of Polymer Containing a Single Type of Nucleotide (Homopolymers) Use of Mixed Polymers with Random Sequences (Heteropolymers) Use of Mixed Polymers with Defined Sequences (Heteropolymers) Use of Trinucleotides in Filter Binding (Minimessengers) Genetic Code is Universal Colinearity of Gene Structure and its Polypeptide Product

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