The Escherichia coli trp promoter has two A + T-rich blocks in the upstream region. The deletion of the segments containing these blocks resulted in a decrease in promoter strength. By replacing the upstream region of trp promoter with one or two large A + T-rich blocks of the major leftward lambda promoter (pL), modified trp promoters (designated let) were constructed, and the transcriptional activities of these promoters towards the expression of the human interferon-gamma gene were measured. The let promoters which contain one (designated letI) or two (designated letII) A + T-rich blocks were about 6 times (at the levels of interferon activity produced) or about 3 times (at the levels of mRNA synthesized de novo) stronger than the wild-type trp promoter. The transcription from the letI promoter was controlled both by the trpR-coded repressor and the cI-coded repressor of phage lambda.
Adenine Base Composition