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How many genes are required for a microorganism?
The smallest known cellular genome is
that of Mycoplasma genitalium, with only 480
protein-coding genes and 37 RNA genes in 580
kb of DNA. However, not all of these genes are
essential. Hutchison et al. (1999) determined by
global transposon mutagenesis that 1354 of
2209 insertions into genes were not lethal to
the organism. The results suggested that 265–
350 of the 480 genes are essential under laboratory
conditions. The limited capacity formetabolism
in M. genitalium is compensated for by a
greater dependence on the transport of
molecules from the extracellular environment
into the cell, mainly by ABC transporters. An
ABC transporter is a heterotrimeric transport
system made up of a specific ligand-binding
subunit, a permease, and an ATP-binding protein.