In vitro synthesis of the first dipeptide of the beta subunit of Escherichia coli RNA polymerase.

Abstract
Plasmids pNF1337 and pNF1341, which contain part of the L10 operon including the RNA polymerase .beta.-subunit gene, were used as templates in vitro to investigate expression of the .beta.-subunit gene. For these studies, the synthesis of the 1st dipeptide of the .beta.-subunit, fMet-Val, was measured instead of that of the entire protein. By using this dipeptide system, the effects of RNA polymerase holoenzyme and L factor (nusA gene product) on fMet-Val synthesis was studied and the relative effects of the primary and secondary promoters in the L10 operon on expression of the .beta.-subunit gene were compared. The inhibitory effect of RNA polymerase on .beta.-subunit synthesis and the stimulatory effect of L factor occur before formation of the 1st dipeptide bond. In this in vitro system, the secondary promoters account for about 50% of the total fMet-Val synthesized. Although the primary promoter is sensitive to guanosine 5''-diphosphate 3''-diphosphate in vitro, the secondary promoters are not affected by this nucleotide.

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