Fig. 1. Binding of different DNA probes by GST–Su(var)3-7. (A) Each lane of a 2.5% agarose gel corresponds to a digest of a 32P-labelled recombinant plasmid. The satellite DNA insert is marked by a star and identified above each lane. The arrows indicate the plasmid fragments used to estimate the relative affinity. (B) Fragments selected by the GST–Su(var)3-7 fusion protein in the absence of poly(dI–dC). Same reaction and probe as in (A). (C) Western blot of the GST–Su(var)3-7 constructs containing seven (lane 2) or six (lane 1) zinc fingers. Both lanes show a minor band of the correct size (110 and 100 kDa, respectively). The major products are truncated proteins, one of 80 kDa (corresponding to a protein with five zinc fingers) and one of 45 kDa (ending just after the second finger). (D) Competition for binding of labelled plasmid pBS(353 bp) by GST–Su(var)3-7. The binding reaction mixtures contain poly(dI–dC) at a final concentration of 0.1 µg/µl and ∼10 ng of labelled plasmid, and 0, 1.0 or 10.0 µg of the same, but unlabelled, digested plasmid was added. In this experiment, the pBS(353 bp) plasmid was cut with EcoRI, HindIII and DdeI, the latter splitting the insert into two fragments.