Analysis of cytadherence-deficient, GapA-negative Mycoplasma gallisepticum strain R

Comparison of the phenotypic expression of Mycoplasma gallisepticum strain R low (passage 15) to that of strain R high (passage 164) revealed that three proteins, i.e., the cytadhesin molecule GapA, a 116-kDa protein (p116), and a 45-kDa protein (p45), are missing in strain R high. Sequence analysis confirmed that the insertion of an adenine 105 bp downstream of the gapA translational start codon resulted in premature termination of translation in R high. A second adenine insertion had also occurred at position 907. Restoration of expression of wild-type gapA in R high (clone designated GT5) allowed us to evaluate the extent to which the diminished cytadherence capacity could be attributed to GapA alone. The results indicated that GT5 attached to the same limited extent as the parental R high, from which it was derived. The cytadherence capability of the parental R high was not restored solely by gapA complementation alone, indicating that either p116 or p45 or both may play a role in the overall cytadherence process. The gene encoding p116 was found to be immediately downstream of gapA in the same operon and was designated crmA. This gene exhibited striking homology to genes encoding molecules with cytadhesin-related functions in both Mycoplasma pneumoniae and Mycoplasma genitalium. Transcriptional analysis revealed that crmA is not transcribed in R high. We are currently constructing a shuttle vector containing both the wild-type gapA and crmA for transformation into R high to assess the role of CrmA in the cytadherence process.