FIG. 4.

Transcription factors in B-lymphoid cells bind to the E-box-containing −59/−53 region of the LRS. (A) A ³²P-labelled double-stranded oligonucleotide corresponding to the −73 to −29 LRS region was incubated with nuclear extracts from DG75 cells and subjected to EMSA. Lane 1 shows the binding pattern obtained with the nuclear extract. Competition reactions was carried out as indicated below the autoradiogram and described in Materials and Methods. Six complexes (indicated by solid arrows) are considered specific. Three complexes were shown to interact with the ATF/CRE site in the LRS and are designated ATF/CRE (bands remaining after competition with an LRS fragment that contained a mutated ATF/CRE site). The other three complexes interacted with the −59/−53 sequence in the LRS (bands remaining after competition with an LRS fragment that contained a mutated −59/−53 sequence). One unspecific band that was not abolished by competition with unlabelled probe is indicated by a dotted arrow. (B) Nucleotide sequences of the double-stranded oligonucleotides used in the competition experiment. Binding sites conforming to Sp, ATF/CRE, and E-box consensus sequences are boxed, and mutated nucleotides are underlined.