Nucleotide sequence of the MgPa (mgp) operon of Mycoplasma genitalium and comparison to the P1 (mpp) operon of Mycoplasma pneumoniae

Abstract

The attachment of Mycoplasma genitalium and Mycoplasma pneumoniae to ciliated epithelium involves two surface proteins designated MgPa and P1, respectively. We have previously cloned and sequenced the P1 (mpp) operon of M. pneumoniae, and report here the use of P1-derived probes to clone and sequence a 10.4-kb region of M. genitalium DNA that, by analogy to the P1 operon, contains the MgPa (mgp) operon. The deduced amino acid sequences of the 29-kDa (ORF-1), MgPa (160-kDa) and 114-kDa (ORF-3) proteins of the MgPa operon show extensive homologies with those of the 28-kDa, P1 (170-kDa) and 130-kDa proteins, respectively, encoded by the P1 operon. The common features and homology of these operons are consistent with previous observations that the MgPa and P1 proteins share cross-reactive epitopes, as well as similar biological function. The gene order of the MgPa operon is ORF-1, MgPa, ORF-3, with intervening regions of 6 and 1 nt, respectively. A consensus ribosome-binding site (RBS) sequence is found before ORF-1 and a sequence indicative of a transcription terminator is located beyond ORF-3; the absence of such sequences adjacent to the MgPa gene suggests that the operon is transcribed as a polycistronic message. The RBS sequence is followed by sequences of dyad symmetry that have the potential to form two alternative stem-and-loop structures, which could be involved in controlling initiation of translation.