Journal of Bacteriology, August 1999, p. 4978-4985, Vol. 181, No. 16
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Department of Microbiology, University of Georgia, Athens, Georgia 30602
Received 1 March 1999/Accepted 7 June 1999
Mycoplasma pneumoniae adherence to host cells is a
multifactorial process that requires the cytadhesin P1 and additional
accessory proteins. The hmw gene cluster consists of the
genes p30, hmw3, and hmw1, the
products of which are known to be essential for cytadherence, the
rpsD gene, and six open reading frames of unknown function.
Putative transcriptional terminators flank this locus, raising the
possibility that these genes are expressed as a single transcriptional
unit. However, S1 nuclease protection and primer extension experiments
identified probable transcriptional start sites upstream of the
p32, p21, p50, and rpsD
genes. Each was preceded at the appropriate spacing by the
10-like
sequence TTAAAATT, but the
35 regions were not conserved.
Analysis of the M. pneumoniae genome sequence indicated
that this promoter-like sequence is found upstream of only a limited
number of open reading frames, including the genes for P65 and P200,
which are structurally related to HMW1 and HMW3. Promoter deletion
studies demonstrated that the promoter-like region upstream of
p21 was necessary for the expression of p30 and
an hmw3-cat fusion in M. pneumoniae, while deletion of the promoter-like region upstream of p32 had no
apparent effect. Analysis by reverse transcription-PCR confirmed
transcriptional linkage of all the open reading frames in the
hmw gene cluster. Taken together, these findings suggest
that the genes of this locus constitute an operon expressed from
overlapping transcripts.
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