Transcription factor USF from duck erythrocytes transactivates expression of the histone H5 gene in vitro by interacting with an intragenic sequence.

The duck histone H5 gene contains a 12 base pair (bp) sequence motif within the coding region, which shows homology in 10 out of 12 bp with the consensus sequence of the USF binding site in the Ad2ML-promoter. The functional equivalent of transcription factor USF, partially purified from whole cell extracts of duck erythrocytes (EUSF), was shown to interact with this intragenic sequence. Electrophoretic mobility shift analyses revealed the selective formation of a complex between this protein fraction and the duck H5 gene. Footprint assays with DNase I delineated specific binding to the intragenic sequence outlined above. Moreover this protein fraction, containing EUSF, transactivates the expression of the duck H5 gene in vitro and elimination of the USF-consensus sequence leads to a loss of stimulation but retains the basic transcription of the gene. These results suggest an as yet unknown functional role of EUSF in the expression of the H5 gene of the duck.