Purification and characterization of a protein binding to the SP6 kappa promoter. A potential role for CArG-box binding factor-A in kappa transcription.

A protein interacting with an A-T-rich region that is a positive control element within the SP6 kappa promoter was purified and identified as CArG-box binding factor-A. The purified protein was shown to interact specifically with the coding strand of single-stranded DNA and, with lower affinity, with double-stranded DNA. A mutation that inhibited binding of the protein to the A-T-rich region also aborted the transcriptional stimulatory effect of the region. Two Ets proteins, PU.1 and elf-1, that have previously been shown to bind to an adjacent DNA element were shown to physically interact with CArG-box binding factor-A. An antiserum raised against the protein recognized two different forms indicating either that different splice-forms of CArG-box binding factor-A are expressed, or that the protein is subject to post-translational modification.