Nucleotide sequence of the P1 attachment-protein gene of Mycoplasma pneumoniae

Abstract

The specific attachment of Mycoplasma pneumoniae to the respiratory ciliated epithelium is mediated by a surface protein designated P1. The nucleotide (nt) sequence of the P1 attachment-protein gene has been determined and the amino acid (aa) sequence deduced. mRNA and cDNA sequencing confirm that this gene is transcribed in M. pneumoniae. The predicted amino acid sequence matches the N-terminal 12 aa residues of P1 protein from M. pneumoniae [Jacobs et al., J. Gen. Microbiol. 133 (1987) 2233-2236] beginning with Asn at aa position 60, where aa 1 represents the first codon of the open reading frame (ORF). Notably, the Trp at aa position 69 aligns with a UGA codon deduced from the nucleotide sequence, providing supporting evidence that UGA is read as Trp rather than stop in M. pneumoniae. Analysis of the first 59 aa suggests that it is probably a leader sequence that is processed to yield the mature protein. The codons of the mature P1 protein sequence represent 1568 aa with a calculated Mr of 169,758. A unique feature of this protein sequence is the lack of cysteine, and this was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of M. pneumoniae proteins metabolically labeled with radioactive cysteine or methionine. This study has revealed that the 4881 nt of the P1 structural gene are flanked by ORFs, and there are no obvious ribosome-binding sites or transcription termination sequences in the immediately adjacent regions. This suggests that the P1 gene is transcribed as part of a larger polycistronic message. In addition, a number of untranscribed and therefore nonfunctional P1 epitope sequences were found in the M. pneumoniae genome; their purpose remains unknown.