Spi-B Transcription Factor (SPIB)

SPI1 and SPIB are members of a subfamily of ETS transcription factors. ETS proteins share a conserved ETS domain that mediates specific DNA binding. SPIB and SPI1 bind to a purine-rich sequence, the PU box (5-prime-GAGGAA-3-prime).The deduced 262-amino acid protein is 43% identical to SPI1. It has a basic C terminus that is 67% identical to that of SPI1, as well as an acidic, proline-rich N-terminal domain. Gel retardation and competition binding analyses confirmed that SPIB interacts with PU boxes. Reporter analyses showed that SPIB encodes a PU box-specific transcription activator. Northern blot analysis revealed expression of a major 1.5-kb transcript, as well as minor 2.8- and 3.7-kb transcripts, in a B-lymphoid cell line and lower expression in promyelocytic and monocytic cell lines.