| Mycoplasma genitalium has the smallest known genome of any organism which can be grown in pure culture. This makes it a target for study to determine the minimal set of gene functions necessary to sustain life. Little is known about how M. genitalium controls expression of its reduced genome, and it lacks several key features of gene regulation present in bacteria with larger genomes. We sought to characterize gene expression in M. genitalium at the transcriptional level. We found that genes can be grouped into functional units that are separated by promoters, but rarely by transcription terminators. A lack of discrete and efficient transcription termination often causes functionally unrelated genes to be cotranscribed. These observations suggest that a loss of transcription terminators has caused a trend towards constitutive gene expression in this reduced genome.; Many genes in M. genitalium can be functionally grouped through the identification of phylogenetically conserved gene clusters. A global map of promoters in M. genitalium could help to functionally classify the twenty percent of genes for which orthologs have not been identified in other organisms, as determined by COG (clusters of orthologous groups) methodology. We showed the efficacy of an RNA ligase-mediated rapid amplification of complementary DNA ends approach for such a mapping. This mapping would also help to characterize promoter sequences, identify translation start codons, and avoid unwanted polar effects of introduced mutations. |
