A 135-kilodalton surface antigen of Mycoplasma hominis PG21 contains multiple directly repeated sequences.

A monoclonal antibody was used to characterize a 135-kDa surface-located membrane protein (Lmp1) generally present in Mycoplasma hominis strains. The monoclonal antibody, 552, was applied to identify the corresponding gene in an expression library of M. hominis PG21 DNA. The M. hominis PG21 lmp1 gene was sequenced, and its gene product was characterized with the goal of elucidating the structure and function of Lmp1. A total of 7,196 bp in the lmp1 region was sequenced. An open reading frame of 4,032 bp, encoding a protein of 1,344 amino acids with a calculated molecular weight of 147,000, was identified. Analysis of the deduced amino acid sequence predicted a hydrophilic protein with a basic pI (10.0). The N-terminal 24 amino acids were a typical leader sequence. Downstream from the first 726 nucleotides, six similar direct repeats of 471 nucleotides were found. In repeat 7, a single-base substitution, C-->A, gave rise to the stop codon of lmp1. Thus, the C-terminal 945 amino acids were encoded by the 471-bp direct repeats. As evidenced by Southern blot analysis, the gene encoding the 135-kDa antigen is part of a multigene family. One of the genes, lmp2, was situated directly downstream from lmp1 where the direct repeats continued.