Identification of a new variable sequence in the P1 cytadhesin gene of Mycoplasma pneumoniae: Evidence for the generation of antigenic variation by DNA recombination between repetitive sequences

A Mycoplasma pneumoniae cytadhesin P1 gene with novel nucleotide sequence v ariation has been identified. Four clinical strains of M. pneumoniae were f ound to carry this type of pi gene. This new P1 gene is similar to the know n group II P1 genes but possesses novel sequence variation of approximately 300 bp in the RepMP2/3 region. The position of the new variable region is distant from the previously reported variable regions known to differ betwe en group I and II P1 genes. Two sequences closely homologous to this new va riable region were found within the repetitive sequences outside the P1 gen e of the M. pneumoniae M129 genome. This suggests that the new P1 gene was generated by DNA recombination between repetitive sequences and the P1 gene locus. The finding of this new type of P1 gene supports the hypothesis tha t the repetitive sequences of the M, pneumoniae genome serve as a reservoir to generate antigenic variation of the cytadhesin P1 gene.