Chapter 14, Problem 29P

Streptococcus parasanguis is a bacterial species that initiates dental plaque formation by adhering to teeth. To investigate ways to eliminate plaque, researchers constructed a plasmid, depicted in the figure shown, to mutagenize S. parasanguis. The key features of this plasmid include rep^ts A (a temperature-sensitive origin of replication), kan^r (a gene for resistance to the antibiotic kanamycin), and the transposon IS256. This transposon contains the erm gene for resistance to the antibiotic erythromycin. IS256 transposes in S. parasanguis thanks to a gene encoding a transposase enzyme that moves all DNA sequences located between the transposon’s inverted repeats (IRs).

a.	How could the researchers use this plasmid as a mutagen? Consider how they could get the transposon into the bacteria, and how they could identify strains that had new insertions of IS256 into S. parasanguis genes. Your answer should explain why the plasmid has two different antibiotic resistance genes as well as a temperature-sensitive origin of replication.
b.	Why would the researchers use this plasmid as a mutagen?
c.	If the investigators found a mutant strain of S. parasanguis that was defective in plaque formation, how could they identify the affected gene?