Transcription of the alpha A-globin gene of the duck. Development of a homologous in vitro system and identification of trans-acting factors.
A homologous in vitro transcription system was developed in which the alpha A-globin gene of the duck was faithfully transcribed. Whole-cell extracts from duck erythrocytes were separated into fractions A, B, C and D by consecutive elution from phosphocellulose columns and were individually reconstituted in run-off transcription assays. Fractions A, C and D were required to achieve faithful initiation on the alpha A-globin gene. The latter fractions were mutually interchangeable with comparable fractions from HeLa cells. A fourth fraction, B, was not required but enhanced basal transcription when reconstituted with fractions A, C and D or a very low amount of HeLa whole-cell extract which by itself did not yield a detectable signal. Fraction B from duck erythrocytes was further purified by chromatography on DEAE-Sephadex and was shown to contain two trans-acting factors. One of these differentially acts on the alpha A-globin gene of the duck. The other component from duck erythrocytes surprisingly resembles the upstream stimulatory factor, previously isolated from HeLa cells. This latter protein binds to and trans-activates the adenovirus 2 major late promoter, but is not involved in the transcription of the alpha A-globin gene.