TABLE 3.

Properties distinguishing mollicutes from other eubacteria^a

Property	Mollicutes	Other eubacteria
Cell wall	Absent	Present
Plasma membrane	Cholesterol present in most species	Cholesterol absent
Genome size	580–2,220 kb	1,050–>10,000 kb
G+C content of genome	23–40 mol%	25–75 mol%
No. of rRNA operons	1 or 2b	1–10
5S rRNA length	104–113 ntc	>114 nt
No. of tRNA genes	30 (M. capricolum), 33 (M. pneumoniae)	84 (B. subtilis), 86 (E. coli)
UGA codon usage	Tryptophan codon in Mycoplasma, Ureaplasma, Spiroplasma, Mesoplasma	Stop codon
RNA polymerase	Rifampin resistant	Rifampin sensitive

^aAdapted from reference 359. 

^bThree rRNA operons in Mesoplasma lactucae (56). 

^cnt, nucleotides.