TITLE:
Impact of Sequence Non-Identities on Recombination within the pil System of Neisseria gonorrhoeae
AUTHORS:
Stuart A. Hill, Jenny Wachter
KEYWORDS:
Recombination, Antigenic Variation, Pilin, Sequence Heterogeneity
JOURNAL NAME:
Open Journal of Genetics,
Vol.4 No.3,
June
27,
2014
ABSTRACT: Neisseria
gonorrhoeae engages in extensive intra-cellular gene conversion between the PilE-expression locus
(pilE) and the
transcriptionally-silent pil gene
copies (pilS). In silico analyses were applied to investigate the extent of
sequence heterogeneity between the various pilS gene copies. Analysis of synonymous and non-synonymous substitutions between
the different pilS genes indicated
that relatively few amino acid changes would occur due to nucleotide
polymorphisms towards the 5’ end of the pilS genes whereas more frequent amino acid substitutions would be incorporated
within the “hypervariable” region. The lack of non-synonymous substitutions at
the 5’ end of the genes was found to be under selective pressure as indicated
by a positive DT score utilizing
the Tajima test. The presence or absence of mismatch repair appeared to only
impact recombination when non-identical DNAs recombined via the DNA
transformation route, where small pil sequence heterogeneities were sufficient to terminate recombination tracts,
with these sequence constraints being relieved in cells carrying a mutS mutation. Therefore, the data
indicate that the effect of sequence heterogeneity on recombination within the pil system appears to depend upon the
context with which the non-identical DNAs recombine.