The CReT plasmid pLSGETS101spc, comprised of the B.
subtilis conjugational plasmid pLS20 and the pBR322
sequence, was constructed by following 3 steps from (i) to
(iii) as illustrated in Fig. 2a: In step (i), the HindIII fragment of
pLS20cat carrying the cat gene was cloned into the unique
HindIII site of pGETS109 (Tomita et al., 2004b); this yielded
the Cm-resistant plasmid pBEAZ203 cloned in RM125. In step
(ii), pBEAZ208 carries a Spec resistance gene (spc) between
tet-half and amp-half of the pBR322 sequence (see also Fig. 1).
It was linearizedwith PvuII and ligated with the blunt-ended BglII
site of pBEAZ203 to produce pBEAZ211. Finally in step (iii),
pBEAZ211 was linearized with PmaCI and used to transform
BEST21274. As a result of homologous recombination between
linear pBEAZ211 and the residential pLS20cat, BEST21278
carrying pLSGETS101spc was selected by Spec and Cm. The
ability of conjugational transfer of pLSGETS101spc was measured
using our standard assay (Itaya et al., 2006).