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Infect. Immun., 07 1997, 2629-2639, Vol 65, No. 7
MK Yeung and PA Ragsdale
The nucleotide sequence of the chromosomal DNA flanking the Actinomyces
naeslundii (formerly A. viscosus) T14V type 1 fimbrial structural subunit
gene (fimP) was determined. Six open reading frames (ORFs), in the order 5'
ORF3, ORF2, ORF1,fimP, ORF4, ORF5, ORF6 3', were identified. ORF1 encoded a
protein of 408 amino acid residues (Mr = 39,270) and had significant
sequence homology with the A. naeslundii T14V type 1 and A. naeslundii
WVU45 type 2 fimbrial structural subunits. An in-frame fusion of ORF1 to
the malE gene of the expression vector, pMAL-c2, yielded a protein that was
immunostained with antibodies raised against the maltose binding protein
and A. naeslundii T14V whole bacteria. Digestion of the fusion protein with
factor Xa released a protein (apparent molecular mass of 34 kDa) that was
immunostained only with the antibody directed against A. naeslundii T14V
whole bacterial cells. Integration plasmids carrying a kanamycin resistance
gene (kan) that was used to substitute for ORF1 or for DNA fragments
internal to the coding region of the other five ORFs were used to transform
A. naeslundii T14V. Neither type 1 fimbriae nor the 65-kDa fimbrial
structural subunit was detected in mutants obtained by allelic replacement
of ORF1 or ORF2. Mutants obtained by allelic replacement of ORF3 or ORF4
expressed only the 65-kDa fimbrial structural subunit. These mutants did
not bind, in vitro, to proline- rich proteins that serve as the receptors
for Actinomyces type 1 fimbriae. In contrast, a mutant in which the
integration plasmid DNA had been inserted at a site close to the carboxyl
terminus of ORF6 expressed type 1 fimbriae and had adherence properties
similar to those observed in the wild-type strain. These results
demonstrate the existence of additional genes near fimP that are likely to
be involved in the synthesis and function of cell surface fimbriae of A.
naeslundii T14V.
Copyright © 1997, American Society for Microbiology
Synthesis and function of Actinomyces naeslundii T14V type 1 fimbriae require the expression of additional fimbria-associated genes
Department of Pediatric Dentistry, The University of Texas Health Science Center at San Antonio, 78284, USA. Yeung@uthscsa.edu
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