Biography:
Norman Harold Horowitz (right) was born on March 19, 1915 in Squirrel hill, Pittsburgh and died on June 1, 2005. Urs Leupold (left) was born on July 19, 1923 - October 9, 2006 and were both geneticists. Both of them are well known for the new studies of bearing one-gene, one-enzyme hypothesis that was proposed by George Wells Beadle in the US in 1941. Their new discovery of the hypothesis, using E.coli and Neurospora, helped them to make it more perfect and understandable.
The hypothesis one-gene one-enzyme, proposed by George Wells Beadle in the US in 1941, is the theory that each gene directly produces a single enzyme, which consequently affects an individual step in a metabolic pathway. Horowitz and Leupold came up with new questions and arguements based the hypothesis. Their question was "are there any grounds for suspecting that these mutants may not represent mutations of unifunctional genes?". They argued that based on the fact that not all of the mutations which are produced can be defected by the methods employed for this purpose.
Methods: To test out their hypothesis, they needed a method for detecting the frequency of mutations which cause loss of a dispensable function. So, they decided to use E. coli for it. What they did was they turned E.coli with the expectation of recovering large numbers of temperature mutants by a modified penicillin technique. This method wasn`t precise for this experiment; although temperature-independent mutants were obtained. The method is simply that of plating out U.V.-treated cells on minimal medium and incubating them for 48 hours at 40 degrees. The plates are transferred to 25 degrees for an additional 5 days, and the colonies are picked off and tested.
Results and Conclusion:
The outcome of the E. coli experiment by Horowitz, shows 25% of temperature-dependent lethals involve loss of indispensable functions. The fraction of mutants which is used for larger molecule is even smaller than the fractions lost in the indispensable functions. Also, the enzymatic synthesis of polypeptides with a special metabolic functions, like glutathione. The one gene one enzyme hypothesis shows that not all gene encode a enzyme and that some enzyme are made up of several short polypeptides encoded by two or more genes.
Cited:"Some Studies of Bearing On The One Gene-One Enzyme Hypothesis" Horowitz and Leupold http://isites.harvard.edu/fs/docs/icb.topic100452.files/HorowitzLeupold1952.pdf |
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