Abstract
Initiation of transcription of the Escherichia coli histidine (his) operon in vitro has been analyzed. The DNA of a specialized transducing phage, ø80dhis, was used as a template, and his RNA was measured by RNA/DNA hybridization. Taking advantage of the fact that E. coli RNA polymerase cannot initiate transcription when the nucleoside triphosphates are present at very low (5 muM) concentration, his RNA initiation was primed by dinucleoside monophosphates. It has been found that his RNA synthesis can be stimulated by one of the three dinucleotides CpA, ApA, and ApG. Under these conditions, it is the initiation of his RNA synthesis that is stimulated. Stimulation of his RNA synthesis by the three dinucleotides apparently occurs at a single initiation site, as judged by the nonadditivity of the effects of the three dinucleotides. This was further confirmed by the effect of phosphoribosyltransferase (the first enzyme of histidine biosynthesis, which specifically represses the synthesis of his RNA) on ApA primed RNA synthesis. Addition of his protein results in a sharp decrease of his RNA synthesis, with no effect whatsoever on the levels of RNAa transcribed from other regions of the template. Our data suggest that the 5' -terminal sequence of his RNA made in vitro is ApApG and that the base immediately preceding this sequence is C.
Highlights
Initiation of transcription of the Escherichia coli histidine operon in vitro has been analyzed
It has been found that his RNA synthesis can be stimulated by one of the three dinucleotides CpA, ApA, and ApG
Stimulation of his RNA synthesis by the three dinucleotides apparently occurs at a single initiation site, as judged by the nonadditivity of the effects of the three dinucleotides
Summary
From the Centro di Endocrinologia ed Oncologia Sperimentale de1CNR, II Istituto di Patologia Generale, 2a Facolta di Medicina, UniversitQ di Napoli, Via Sergio Pansini, 5; 80131Naples, Italy. Stimulation of his RNA synthesis by the three dinucleotides apparently occurs at a single initiation site, as judged by the nonadditivity of the effects of the three dinucleotides This was further confirmed by the effect of phosphoribosyltransferase (the first enzyme of histidine biosynthesis, which represses the synthesis of his RNA) on ApA primed RNA synthesis. Since the three dinucleotides appear to act on the same initiation site, their structures can be used to deduce a possible unique sequence around the starting point of his RNA transcription Under these conditions, the influence of effecters of his RNA synthesis can be studied with much more precision. In this way we have confirmed the already reported [4] repression by phosphoribosyltransferase, the first histidine biosynthetic enzyme, of the in vitro transcription of the E. coli hisoperon
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