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== M. leprae genome == |
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[[Image:Blisters01.jpg]]In leprosy both the reference points for measuring the [http://en.wikipedia.org/wiki/Incubation_period incubation period] and the times of infection and onset of disease are difficult to define; the former because of the lack of adequate immunological tools and the latter because of the insidious nature of the onset of leprosy. Even so, several investigators have attempted to measure the incubation period for leprosy. The minimum incubation period reported is as short as a few weeks and this is based on the very occasional occurrence of leprosy among young infants. <ref>Montestruc E & Berdonneau Bull Soc Pathol Exot Filiales 1954; 47:781–783</ref> The maximum incubation period reported is as long as 30 years, or over, as observed among war veterans known to have been exposed for short periods in endemic areas but otherwise living in non-endemic areas. It is generally agreed that the average incubation period is between 3 to 5 years. |
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''Mycobacterium leprae'' has the longest doubling time of all known bacteria and has thwarted every effort at culture in the laboratory. Comparing the [[genome]] sequence of ''Mycobacterium leprae'' with that of [[Mycobacterium tuberculosis]] provides clear explanations for these properties and reveal an extreme case of reductive [[evolution]]. Less than half of the genome contains functional [[genes]]. Gene deletion and decay appear to have eliminated many important [[metabolic]] activities, including [[siderophore]] production, part of the oxidative and most of the [[microaerophilic]] and [[anaerobic]] [[respiratory]] chains, and numerous [[catabolic]] systems and their regulatory circuits. <ref>Cole S T, Brosch R, Parkhill J et al. Nature 1998; 393: 537-544.</ref> |
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The genome sequence of a strain of Mycobacterium leprae, originally isolated in Tamil Nadu and designated 'TN', has been completed recently. The sequence was obtained by a combined approach, employing automated [[DNA]] sequence analysis of selected [[cosmids]] and whole-genome 'shotgun' clones. After the finishing process, the genome sequence was found to contain 3,268,203 base-pairs (bp), and to have an average G+C content of 57.8%, values much lower than the corresponding values for ''M. tuberculosis'', which are 4, 441,529 bp and 65.6% G+C. There are 1500 genes which are common to both ''M. leprae'' and ''M. tuberculosis''. The comparative analysis suggests that that both mycobacteria derived from a common ancestor and, at one stage, had gene pools of similar size. Downsizing from a genome of 4.42 Mb, such as that of ''M. tuberculosis'', to one of 3.27 Mb would account for the loss of some 1200 [[protein]] coding sequences. There is evidence that many of the genes were present in the genome of ''M. leprae'' have truly been lost. <ref>Cole S T, Eiglmeier K, Parkhill J et al. Nature 2001; 409: 1007-1011.</ref> |
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Information from the completed genome can be useful to develop diagnostic skin tests, understanding the mechanism of nerve damage, drug resistance and to identify novel drug targets for rational design of new therapeutic regimens and drugs to treat leprosy and its complications. |
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Latest revision as of 15:13, 29 March 2007
M. leprae genome[edit]
Mycobacterium leprae has the longest doubling time of all known bacteria and has thwarted every effort at culture in the laboratory. Comparing the genome sequence of Mycobacterium leprae with that of Mycobacterium tuberculosis provides clear explanations for these properties and reveal an extreme case of reductive evolution. Less than half of the genome contains functional genes. Gene deletion and decay appear to have eliminated many important metabolic activities, including siderophore production, part of the oxidative and most of the microaerophilic and anaerobic respiratory chains, and numerous catabolic systems and their regulatory circuits. [1]
The genome sequence of a strain of Mycobacterium leprae, originally isolated in Tamil Nadu and designated 'TN', has been completed recently. The sequence was obtained by a combined approach, employing automated DNA sequence analysis of selected cosmids and whole-genome 'shotgun' clones. After the finishing process, the genome sequence was found to contain 3,268,203 base-pairs (bp), and to have an average G+C content of 57.8%, values much lower than the corresponding values for M. tuberculosis, which are 4, 441,529 bp and 65.6% G+C. There are 1500 genes which are common to both M. leprae and M. tuberculosis. The comparative analysis suggests that that both mycobacteria derived from a common ancestor and, at one stage, had gene pools of similar size. Downsizing from a genome of 4.42 Mb, such as that of M. tuberculosis, to one of 3.27 Mb would account for the loss of some 1200 protein coding sequences. There is evidence that many of the genes were present in the genome of M. leprae have truly been lost. [2]
Information from the completed genome can be useful to develop diagnostic skin tests, understanding the mechanism of nerve damage, drug resistance and to identify novel drug targets for rational design of new therapeutic regimens and drugs to treat leprosy and its complications.