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Infection and Immunity, October 2000, p. 5889-5900, Vol. 68, No. 10
Department of Microbiology, University of
Alabama at Birmingham, Birmingham, Alabama,1
and Aventis Pasteur Laboratories, Swiftwater,
Pennsylvania2
Received 15 November 1999/Returned for modification 31 March
2000/Accepted 26 April 2000
Pneumococcal surface protein A (PspA) is a serologically variable
protein of Streptococcus pneumoniae. Twenty-four diverse alleles of the pspA gene were sequenced to investigate the
genetic basis for serologic diversity and to evaluate the potential of diversity to have an impact on PspA's use in human vaccination. The 24 pspA gene sequences from unrelated strains revealed two major allelic types, termed "families," subdivided into clades. A
highly mosaic gene structure was observed in which individual mosaic
sequence blocks in PspAs diverged from each other by over 20% in many
cases. This level of divergence exceeds that observed for blocks in the
penicillin-binding proteins of S. pneumoniae or in many
cross-species comparisons of gene loci. Conversely, because the mosaic
pattern is so complex, each pair of pspA genes also has
numerous shared blocks, but the position of conserved blocks differs
from gene pair to gene pair. A central region of pspA,
important for eliciting protective antibodies, was found in six clades,
which each diverge from the other clades by >20%. Sequence
relationships among the 24 alleles analyzed over three windows were
discordant, indicating that intragenic recombination has occurred
within this locus. The extensive recombination which generated the
mosaic pattern seen in the pspA locus suggests that natural
selection has operated in the history of this gene locus and
underscores the likelihood that PspA may be important in the interaction between the pneumococcus and its human host.
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Diversity of PspA: Mosaic Genes and Evidence for
Past Recombination in Streptococcus pneumoniae
*
Corresponding author. Mailing address: Department of
Microbiology, BBRB654, University of Alabama at Birmingham, Birmingham, AL 35294. Phone: (205) 934-0570. Fax: (205) 975-5480. E-mail: hollings{at}uab.edu.
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