| Research Abstract |
The RNA polymerase holoezyme of Escherichia coli is composed of core enzyme with the subunit structure of alpha_2betabeta' and one of seven different molecular species of sigma subunits, each recognizing a different promoter sequence. The promoter selectivity of RNA polymerase is further modulated after interaction with one or two of more than 100 different species of trans-acting protein and nucleotide factors, generally designated as transcription factors, with the regulatory activities of transcriprion. The RNA polymerase activity is also modulated by cis-acting regulatory DNA signals generally located upstream of promoters. The contact sites on RNA polymerase subunits have been determined for more than 30 transcription regulatory protein or nucleotide factors. Based on the contact sites, we proposed to classify the transcription factors into four groups : clss-I(alpha contact), II(sigma contact), III(beta contact) and VI(beta' contact) factors. The contact sites estimated from mutant studies have been confirmed using a new tool of chemical reagent, Fe-BABE,with contact-dependent cleavage activity of DNA and proteins.
Since the total number of RNA polymerase core enzyme is fixed at a low and constant level characteristic of the rate of cell growth, the concentrations of each from holoenzyme and ezch RNA polymerase-transcription factor complex are subject to fluctuation depending on growth-dependent variations in the concentrations of each sigma subunit and each transcription factor. Variation in the molecular arhitecture of transcription apparatus was analyzed during growth transition of E.coli from exponentially growing to stationary phase. Accordingly, the species and order of gene transcription among about 4,000 genes on the E.coli chromosome change depending on the cell growth conditions.
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