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

AUTOR(ES)

Peacock, S

RESUMO

Plasmids pNF1337 and pNF1341, which contain part of the L10 operon including the RNA polymerase beta-subunit gene, have been used as templates in vitro to investigate expression of the beta-subunit gene. For these studies, the synthesis of the first dipeptide of the beta subunit, fMet-Val, was measured instead of that of the entire protein. By using this dipeptide system, we studied the effects of RNA polymerase holoenzyme and L factor (nus A gene product) on fMET-Val synthesis and compared the relative effects of the primary and secondary promoters in the L10 operon on expression of the beta-subunit gene. The results show that the inhibitory effect of RNA polymerase on beta-subunit synthesis and the stimulatory effect of L factor occur before formation of the first 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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