Schematic representation of construction of synthetic tandem arrays.
(a) Step one includes amplification
of either a 2,078 bp 21-II-lacOgal4 12-mer or a 343 bp 21-I-tetO dimer
by rolling circle amplification (RCA) reaction up to 1–3 kb
fragments. (b) Step two includes construction of long alphoid arrays
by transformation-associated recombination (TAR) cloning in yeast.
The RCA-amplified fragments are cotransformed into yeast cells along
with the MluI-linearized RCA-Sat43 vector (the MluI restriction site
is located between the hooks). This vector contains a BAC cassette
(a BAC replicon and a Clm marker), a YAC cassette
(a selectable marker HIS3, a centromere sequence CEN6 from yeast chromosome VI, and yeast origin of replication ARSH4), and a mammalian marker Bsr (the blasticidin gene)
that allows the vector to propagate in yeast, bacterial, and mammalian
cells and alphoid-specific hooks of 40 bp each (Ebersole et al. 2005).
Recombination of the RCA-amplified fragments accompanied by their
recombination with the hooks results in the rescue of long arrays
as circular YAC/BACs, and 40 kb α21-I-tetO and 40 kb α21-II-lacOgal4
arrays were chosen for further experiments. (c) Construction of the
hybrid tetO-CENPB+-lacOgal4-CENPB– array.
Recombination between the arrays accompanied by their recombination
with the vector hooks leads to formation of the hybrid arrays. Ultimately,
a molecule containing a 20 kb lacOgal4 array and 25 kb tetO array
was chosen for HAC formation.