9.1 Quiz

Label the following image.

Most E. coli promoters interact with _____ polymerase, the major initiating form of the bacterial enzyme.

In E. coli, there are [blank_start]6[blank_end] alternative σ-factors in addition to the major “housekeeping” σ-factor, σ70.

One class, represented in E. coli by ___, is unrelated to σ70 and functions differently

Transcription of genes by RNA polymerases containing σ54 is regulated solely by activators whose binding sites in DNA, referred to as [blank_start]enhancers[blank_end], are generally located 80–160 bp [blank_start]upstream[blank_end] from the transcription start site.

Transcription by σ54-RNA Polymerase Is Controlled by Activators That Bind close to the Promoter

Even when enhancers are moved more than a kilobase away from a start site, σ54-activators can activate transcription

Electron microscopy studies have shown that phosphorylated NtrC bound at enhancers and σ54-polymerase bound at the promoter interact directly, forming a [blank_start]loop[blank_end] in the DNA between the binding sites (Figure 9-5). As discussed later in this chapter, this activation mechanism resembles the predominant mechanism of transcriptional activation in [blank_start]eukaryotes[blank_end].

The best-characterized σ54-activator—the [blank_start]NtrC[blank_end] protein

The operator is where the [blank_start]repressor[blank_end] binds.

The [blank_start]promoter[blank_end] is where RNA-Polymerase binds.

Gene expression in both prokaryotes and eukaryotes is regulated primarily by mechanisms that control gene [blank_start]transcription[blank_end].

The first step in the initiation of transcription in E. coli is the binding of a [blank_start]sigma[blank_end]-factor complexed with an [blank_start]RNA polymerase[blank_end] to a [blank_start]promoter[blank_end].

The ___________ of a promoter determines its strength, that is, how frequently different RNA polymerase molecules can bind and initiate transcription per minute.

[blank_start]Repressors[blank_end] are proteins that bind to [blank_start]operator[blank_end] sequences that overlap or lie adjacent to promoters. Binding of a [blank_start]repressor[blank_end] to an operator inhibits transcription initiation or elongation.

Genes transcribed by σ54-RNA polymerase are regulated by activators that bind to enhancers located about 100 base pairs [blank_start]upstream[blank_end] from the start site. When the activator and σ54-RNA polymerase interact, the DNA between their binding sites forms a [blank_start]loop[blank_end]

In [blank_start]two-component regulatory systems[blank_end], one protein acts as a sensor, monitoring the level of nutrients or other components in the environment. Under appropriate conditions, the γ-phosphate of an ATP is transferred first to a [blank_start]histidine[blank_end] in the sensor protein and then to an [blank_start]aspartic acid[blank_end] in a second protein, the response regulator. The phosphorylated response regulator then performs a specific function in response to the stimulus, such as binding to DNA regulatory sequences, thereby stimulating or repressing transcription of specific genes

Transcription in bacteria can also be regulated by control of [blank_start]transcriptional elongation[blank_end] in the [blank_start]promoter-proximal[blank_end] region. This control can be exerted by ribosome binding to the nascent mRNA, as in the case of the E. coli trp operon (see Figure 9-7), or by riboswitches, RNA sequences that bind small molecules, as for the B. subtilis xpt-pbuX operon (see Figure 9-8), to determine whether a stem-loop followed by a string of uracils forms, causing the bacterial RNA polymerase to pause and terminate transcription.