Identification of USF as the ubiquitous murine factor that binds to and stimulates transcription from the immunoglobulin lambda 2-chain promoter.

To study the specificity and identity of NF-lambda 2, a ubiquitous murine nuclear factor that interacts specifically with the promoter of the lambda 2-chain gene and stimulates its transcription, competition experiments were carried out using DNA fragments from various immunoglobulin regulatory elements. The results showed that a fragment containing the H-chain enhancer competed efficiently for the binding of NF-lambda 2. Dissection of the H-chain enhancer revealed that the microE3 motif contributed the competing ability. Additionally, a regulatory region found in the adenovirus major late promoter, which interacts with the human general transcription factor USF, competed very efficiently for binding to NF-lambda 2. This region contains a sequence, CACGTGAC, which is identical to a region within the NF-lambda 2 motif. The pattern of complexes formation using oligonucleotide probes corresponding to the NF-lambda 2 and USF motifs were identical, and they both differed from that displayed by the E3 probes. Antisera against different domains of USF also react specifically with NF-lambda 2 showing that this factor is antigenically related, if not identical, to USF. Furthermore, the activity of the lambda 2 promoter in an in vitro transcription assay was significantly reduced when the nuclear extract used was USF-depleted. Addition of exogenous USF to this extract restored the transcription activity. Therefore, we conclude that NF-lambda 2 is the murine homologue of USF.