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.