(A) Shown is the 30 bp sequence delineating unlabelled
competitor DNAs for the 129B6 polymorphic region. The polymorphic site
is denoted by an asterisk. Fragments a, b and c span the individual
regions shown. These fragments were used for competition as concatemers
of three copies of each 10 bp region. (B) Representative
PhosphorImager-generated autoradiograph of unlabelled co-competition
experiments with different competitor DNAs reacting with 129B6 retinal
extract. The radiolabelled 129B6 full-length probe was incubated in the
presence or absence of unlabelled competitor DNAs. Each competitor DNA
was used at a 150-fold molar excess of potential binding sites.
Competitor a specifically competed Complex 2, while b competed Complex
1, but minimally competed Complex 2. Alternatively, oligo bc efficiently
competed Complex 2. These results suggested Complex 2 was formed with
interactions upstream of the polymorphic site, but may also involve
interactions further downstream of this site.