Table 1. DNA sequences used to investigate DB270/DNA/PU.1 interactions.

Name	Sequence	Reference
λB	5′-GCGAATAAAAGGAAGTGAAACCG-3′	(20)
[5′]AGC	5′-GCGAATAAGCGGAAGTGAAACCG-3′	(23)
SC1	5′-CGGCCAAGCCGGAAGTGAGTGCC-3′	(24)
NS	5′-GCGAATAAGCGAGAGTGAAACCG-3′	(9)

Typical of members of the ETS family of transcription factors, PU.1 recognizes an array of sequences bearing a central 5′-GGAA-3′ consensus (in bold). High-affinity DNA binding sites for PU.1 in vivo also frequently harbor A-tracks, defined as four or more consecutive AT base pairs (18). AT-selective heterocyclic dications such as DB270 and DB1976 target A-tracks in sequences such as the λB motif (5), a natural PU.1 binding site in the murine Igλ2-4 enhancer. [5′]AGC is derived from the λB motif and has the highest reported affinity for PU.1. SC1 is a non-AT rich sequence that PU.1 recognizes in vitro, while NS is a sequence isomer of [5′]AGC in which the central consensus is mutated to the non-cognate 5′-GAGA-3′.