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J. Bacteriol., Nov 1995, 6201-6210, Vol 177, No. 21
ZM Wei and SV Beer
hrpL of Erwinia amylovora Ea321 encodes a 21.7-kDa regulatory protein,
similar to members of the ECF (extra cytoplasmic functions) subfamily of
eubacterial RNA polymerase sigma factors. hrpL is a single-gene operon in
complementation group VI of the E. amylovora hrp gene cluster. Its product
is required by Ea321 to elicit the hypersensitive response (HR) and to
cause disease. HrpL controls the expression of five independent hrp loci,
including hrpN, which encodes harpin, a proteinaceous elicitor of the HR.
hrpL is environmentally regulated, and its expression is affected by hrpS,
another regulatory gene of the hrp gene cluster of E. amylovora. pCPP1078,
a multicopy plasmid carrying hrpL, is able to restore HR-eliciting ability
to hrpS mutants. A conserved motif was identified upstream of the hrpI and
hrpN operons, which are transcriptionally regulated by hrpL. This conserved
motif shares a high degree of similarity with other biochemically defined
or putative ECF-dependent promoter sequences, including sequences upstream
of Streptomyces coelicolor dagA P2, Pseudomonas aeruginosa algD,
Pseudomonas syringae pv. syringae 61 hrpZ, and P. syringae pv. tomato avrD.
In spite of the similarity between the hrpL genes of E. amylovora and P.
syringae 61, no functional cross-complementation was observed.
Copyright © 1995, American Society for Microbiology
hrpL activates Erwinia amylovora hrp gene transcription and is a member of the ECF subfamily of sigma factors
Department of Plant Pathology, Cornell University, Ithaca, New York 14853, USA.
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