The immunoreactive 116 kDa surface protein of Mycoplasma pneumoniae is encoded in an operon

Sera from 10 patients infected with Mycoplasma pneumoniae were used in Western blot analysis of Triton-X-114-soluble protein preparations of M. pneumoniae. All 10 sera were reactive with a protein antigen of 116 kDa. Sera from another 17 patients were used in Western blot analysis of whole-cell M. pneumoniae proteins; 15 of these sera were reactive with the 116 kDa protein. Trypsin digestion of whole M. pneumoniae cells demonstrated the surface location of this protein. Sequencing of DNA which contained the gene for this protein identified an ORF of 3093 bp encoding a protein with a predicted molecular mass of 116013 Da. The ORF for the 116 kDa protein had 99.8% nucleotide identity with the M. pneumoniae gene G07_orf1030 and 61% nucleotide identity with the Mycoplasma genitalium ORF MG075 of unassigned function. An ORF which was identified 5' to the 116 kDa protein ORF coded for a 16 kDa protein and had 99.8% nucleotide identity with the M. pneumoniae gene G07_orf135 and 58.4% nucleotide identity with the ORF MG074 of M. genitalium. Analysis of mRNA detected a 3.7 kb transcript with a single initiation site 5' to the ORF encoding the 16 kDa protein. The coding sequences for both the 16 kDa protein and the 116 kDa protein were present in this transcript, indicating that they were part of an operon and suggesting a possible functional relationship.