This 1968 study examined the chemical composition of nucleic acids and proteins in several Mycoplasma strains. The researchers isolated and analyzed DNA and RNA from three strains of Mycoplasma laidlawii and one strain of M. mycoides var. mycoides, determining their base compositions using chemical methods. Both DNA species showed extreme adenine-thymine (AT) content with guanine-cytosine (GC) values ranging from 30.0 to 34.4%, indicating similarity between the mycoplasma species. RNA analysis revealed adenine-uracil to guanine-cytosine ratios of 1.17-1.20. The team also corrected previously published amino acid composition data for M. mycoides var. capri, which had been contaminated by precipitated medium proteins due to pH changes during culture growth. The corrected amino acid composition of M. mycoides var. capri closely matched predicted values based on DNA base composition. Similarly, the amino acid composition of M. laidlawii proteins agreed well with values predicted from organisms with similar DNA base composition, validating the relationship between nucleic acid and protein composition in mycoplasmas.

Key findings

• Mycoplasma laidlawii and M. mycoides var. mycoides show extreme AT-rich DNA with GC content of 30.0-34.4%, suggesting close relationship between species
• RNA base composition (A+U:G+C ratio of 1.17-1.20) showed similar patterns across analyzed mycoplasma strains
• Amino acid composition of mycoplasma proteins correlated closely with DNA base composition, consistent with Sueoka's predictions for bacteria with similar GC content
• Previous amino acid analysis of M. mycoides var. capri was erroneous due to precipitation of medium proteins caused by pH decrease during culture growth
• Chemical analysis methods provided more reliable base composition data than physical methods like melting point analysis or density gradient centrifugation