Ms. Lee et al., Insertion-duplication mutagenesis in Streptococcus pneumoniae: Targeting fragment length is a critical parameter in use as a random insertion tool, APPL ENVIR, 64(12), 1998, pp. 4796-4802
To examine whether insertion-duplication mutagenesis with chimeric DNA as a
transformation donor could be valuable as a gene knockout tool fur genomic
analysis in Streptococcus pneumoniae, we studied the transformation effici
ency and targeting specificity of the process by using a nonreplicative vec
tor with homologous targeting inserts of various sizes. insertional recombi
nation was very specific in targeting homologous sites. While the recombina
tion rate did not depend on which site or region was targeted, it did depen
d strongly on the size of the targeting insert in the donor plasmid, in pro
portion to the fifth power of its length for inserts of 100 to 500 bp, The
dependence of insertion-duplication events on the length of the targeting h
omology was quite different from that for linear allele replacement and pla
ces certain limits an the design of mutagenesis experiments. The number of
independent pneumococcal targeting fragments of uniform size required to kn
ock out any desired fraction of the genes in a model genome with a defined
probability was calculated from these data by using a combinatorial theory
with simplifying assumptions. The results shaw that efficient and: thorough
mutagenesis of a large part of the pneumococcal genome should be practical
when using insertion-duplication mutagenesis.