The ORF6 gene product of the P1 operon of Mycoplasma pneumoniae.

The P1 attachment protein gene of Mycoplasma pneumoniae is flanked by two open reading frames with a coding capacity for two proteins of 28 kDa (ORF4) and 130 kDa (ORF6), respectively. An operon-like organization in the order ORF4-P1-ORF6 was proposed by Inamine et al. (11). Instead of an expected 130 kDa protein, two proteins of 40 and 90 kDa were identified as the gene product of ORF6 which might arise from cotranslational cleavage (18). After purification of both proteins, the N-terminal amino acid of the 90 kDa protein was determined. Thus, we identified the putative cotranslational cleavage site before amino acid position 455 (R) (15). Biochemical and immunological studies indicate that both proteins are membrane-associated, exhibiting surface-exposed regions (15). Since a wild-type-derived mutant lacking the 40 as well as the 90 kDa protein shows reduced attachment to host cells we suggest that the ORF6 encodes for two proteins which contribute to proper adherence of M. pneumoniae to host cells.