Identification of novel single-stranded DNA binding proteins recognizing octamer motif.

We have previously identified the region containing transcriptional enhancer in mouse immunoglobulin heavy chain (IgH) gene as an initiation region of DNA replication. The octamer sequence therein has been found to be essential for initiation of DNA replication as well as for transcription. Octamer-binding protein family, including Oct (OTF)-1, 2A, and 2B, bound to the element in double-stranded form. Here we identified in various cells novel proteins which bound to the upper strand of the octamer sequence in the IgH gene. Three proteins of 35, 60, and 125 KDa recognized the sequences. The proteins, which were not recognized by an anti-Oct-1 antibody, may be involved in regulation of the initiation of DNA replication in the IgH gene.