table of contents Proteins that act at specific DNA sequences
bind DNA randomly and then … A series of 2.7-kb plasmids were
constructed with two BbvCI sites separated by varied distances,
from 30 to 75 bp. (Because the products from cutting the
plasmids at one or both sites could not be separated from each
other by electrophoresis, the reactions were studied on 301-bp
fragments with both sites, generated by PCR across the relevant
section of each plasmid.) To minimize local sequence effects,
both sites had the same flanking sequences for 5 bp around the
sites. For each construct, two derivatives were isolated: one
with sites oriented in direct (head-to-tail) repeat so that one
strand carries both copies of the CC sequence and the other both
copies of GC, the targets for R2 and R1, respectively (Fig. 1a);
another with sites in inverted (head-to-head) orientation so
that the two CC sequences are in opposite strands, and likewise
GC (Fig. 1b). For processive action, BbvCI must translocate from
one site to the ot