Implications of high level pseudogene transcription in Mycobacterium leprae

The Mycobacterium leprae genome has less than 50% coding capacity and 1,133 pseudogenes. Preliminary evidence suggests that some pseudogenes are expressed. Therefore, defining pseudogene transcriptional and translational potentials of this genome should increase our understanding of their impact on...

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Bibliographic Details
Published in:	BMC genomics 2009-08, Vol.10 (1), p.397-397
Main Authors:	Williams, Diana L, Slayden, Richard A, Amin, Amol, Martinez, Alejandra N, Pittman, Tana L, Mira, Alex, Mitra, Anirban, Nagaraja, Valakunja, Morrison, Norman E, Moraes, Milton, Gillis, Thomas P
Format:	Article
Language:	eng
Subjects:	Base Sequence Codon, Initiator Codon, Terminator Gene Expression Profiling Gene Expression Regulation, Bacterial Gene Silencing Genes, Bacterial Genetic aspects Genetic transcription Genome, Bacterial Molecular Sequence Data Mycobacterium leprae Mycobacterium leprae - genetics Oligonucleotide Array Sequence Analysis Open Reading Frames Physiological aspects Promoter Regions, Genetic Protein Biosynthesis Pseudogenes Transcription, Genetic
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Summary:	The Mycobacterium leprae genome has less than 50% coding capacity and 1,133 pseudogenes. Preliminary evidence suggests that some pseudogenes are expressed. Therefore, defining pseudogene transcriptional and translational potentials of this genome should increase our understanding of their impact on M. leprae physiology. Gene expression analysis identified transcripts from 49% of all M. leprae genes including 57% of all ORFs and 43% of all pseudogenes in the genome. Transcribed pseudogenes were randomly distributed throughout the chromosome. Factors resulting in pseudogene transcription included: 1) co-orientation of transcribed pseudogenes with transcribed ORFs within or exclusive of operon-like structures; 2) the paucity of intrinsic stem-loop transcriptional terminators between transcribed ORFs and downstream pseudogenes; and 3) predicted pseudogene promoters. Mechanisms for translational "silencing" of pseudogene transcripts included the lack of both translational start codons and strong Shine-Dalgarno (SD) sequences. Transcribed pseudogenes also contained multiple "in-frame" stop codons and high Ka/Ks ratios, compared to that of homologs in M. tuberculosis and ORFs in M. leprae. A pseudogene transcript containing an active promoter, strong SD site, a start codon, but containing two in frame stop codons yielded a protein product when expressed in E. coli. Approximately half of M. leprae's transcriptome consists of inactive gene products consuming energy and resources without potential benefit to M. leprae. Presently it is unclear what additional detrimental affect(s) this large number of inactive mRNAs has on the functional capability of this organism. Translation of these pseudogenes may play an important role in overall energy consumption and resultant pathophysiological characteristics of M. leprae. However, this study also demonstrated that multiple translational "silencing" mechanisms are present, reducing additional energy and resource expenditure required for protein production from the vast majority of these transcripts.
ISSN:	1471-2164 1471-2164