ISOLATION AND CHARACTERIZATION OF A CHICKEN HOMOLOG OF THE SPI-1 PU.1TRANSCRIPTION FACTOR/

Spi-1/PU.1 is a member of the Ets family of transcription factors impo rtant in regulation of hematopoiesis. We have isolated a chicken cDNA homologuous to the mammalian Spi-1/PU.1 gene with an open reading fram e of 250 amino acids (aa). The chicken Spi-1/PU.1 protein is 14 aa and 16 aa shorter than its human and mouse counterparts but is extremely well conserved with 78.8% and 75.2% identity respectively. The carboxy terminal DNA binding region, or ETS binding domain, is 100% identical to that of human and mouse. Some differences with the mammalian homol ogues are seen in the N-terminal part of the protein and in the PEST c onnecting domain. However, the differences are mainly conservative and all the features underlying functional aspects seem preserved. The ma jor discrepancy lies in a 12 aa deletion in an already poorly conserve d part of the PEST sequence. Spi-1/PU.1 transcripts were detected at h igh levels in spleen and Fabricius bursa of chick embryos by Northern blot and in situ hybridization. Our results show that the chicken Spi- 1/PU.1 protein behaves like a bonafide Spi-1/PU.1 transcription factor in its DNA binding and transactivating properties.