Global transposon mutagenesis and a minimal mycoplasma genome

Mycoplasma genitalium with 517 genes has the smallest gene complement of an y independently replicating cell so far identified. Global transposon mutag enesis was used to identify nonessential genes in an effort to Learn whethe r the naturally occurring gene complement is a true minimal genome under La boratory growth conditions. The positions of 2209 transposon insertions in the completely sequenced genomes of M. genitalium and its close relative M. pneumoniae were determined by sequencing across the junction of the transp oson and the genomic DNA. These junctions defined 1354 distinct sites of in sertion that were not Lethal. The analysis suggests that 265 to 350 of the 480 protein-coding genes of M. genitalium are essential under Laboratory gr owth conditions, including about 100 genes of unknown function.