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 organizati on in the order ORF4-P1-ORF6 was proposed by Inamine et al. (11). Inst ead 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 cotrans lational cleavage (18). After purification of both proteins, the N-ter minal amino acid of the 90 kDa protein was determined. Thus, we identi fied the putative cotranslational cleavage site before amino acid posi tion 455 (R) (15). Biochemical and immunological studies indicate that both proteins are membrane-associated, exhibiting surface-exposed reg ions (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 t hat the ORF6 encodes for two proteins which contribute to proper adher ence of M. pneumoniae to host cells.