In Vivo Transcription Dynamics of the Galactose Operon: A Study on the Promoter Transition from P1 to P2 at Onset of Stationary Phase

Abstract

Quantitative analyses of the 5′ end of gal transcripts indicate that transcription from the galactose operon P1 promoter is higher during cell division. When cells are no longer dividing, however, transcription is initiated more often from the P2 promoter. Escherichia coli cells divide six times before the onset of the stationary phase when grown in LB containing 0.5% galactose at 37°C. Transcription from the two promoters increases, although at different rates, during early exponential phase (until the third cell division, OD600 0.4), and then reaches a plateau. The steady-state transcription from P1 continues in late exponential phase (the next three cell divisions, OD600 3.0), after which transcription from this promoter decreases. However, steady-state transcription from P2 continues 1 h longer into the stationary phase, before decreasing. This longer steady-state P2 transcription constitutes the promoter transition from P1 to P2 at the onset of the stationary phase. The intracellular cAMP concentration dictates P1 transcription dynamics; therefore, promoter transition may result from a lack of cAMP-CRP complex binding to the gal operon. The decay rate of gal-specific transcripts is constant through the six consecutive cell divisions that comprise the exponential growth phase, increases at the onset of the stationary phase, and is too low to be measured during the stationary phase. These data suggest that a regulatory mechanism coordinates the synthesis and decay of gal mRNAs to maintain the observed gal transcription. Our analysis indicates that the increase in P1 transcription is the result of cAMP-CRP binding to increasing numbers of galactose operons in the cell population.

Two-level inhibition of galK expression by Spot 42: Degradation of mRNA mK2 and enhanced transcription termination before the galK gene

“…The transcription dynamics for the overall production of the gal transcripts correspond very well with previously reported measurements (16,17). It was demonstrated that the intracellular concentration of cAMP regulates the overall production of the gal transcripts by governing the rate of transcription initiation (17). We found that two types of polarity, type 1 and type 2 (1), were established, depending on the growth period (Fig.…”

Toward Repurposing Ciclopirox as an Antibiotic against Drug-Resistant Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae

“…The amphibolic galETKM operon includes galE (UDP-glucose 4-epimerase), galT (galactose-1-phosphate uridylyltransferase), galK (galactokinase), and galM (galactose mutarotase) under control of two promoters, P1 and P2. During early to late logarithmic growth phase, 70% of the galETKM transcripts are synthesized from the P1 promoter and all four genes are made [35], [57]. However, upon transition from late logarithmic to early stationary phase, 70% of transcripts are from the P2 promoter, which predominately synthesizes galE [35], [57].…”

“…During early to late logarithmic growth phase, 70% of the galETKM transcripts are synthesized from the P1 promoter and all four genes are made [35], [57]. However, upon transition from late logarithmic to early stationary phase, 70% of transcripts are from the P2 promoter, which predominately synthesizes galE [35], [57]. This differential promoter utilization and other posttranscriptional regulation of the galETKM operon using noncoding RNAs allows E. coli to either catabolize galactose or to generate the nucleotide-charged substrates, UDP-galactose or UDP-glucose, depending on cellular needs [35], [58].…”

Understanding the genome-wide transcription response to varying cAMP levels using phenomenological models in bacteria

“…Increasing cAMP levels redirect greater cellular resources towards the expression of transport and metabolic genes (28,41). E.coli cells not only experience cAMP changes across carbon sources (21,42), but cAMP concentrations in the cell vary continuously in response to cell density and growth phases as well (43)(44)(45).…”