Regulation of Gene Expression in Bacteria (Lectures 13–14)

Fill-in-the-blank flashcards covering lac and arabinose operons, cis/trans regulation, promoter architecture, sigma factors, consensus sequences, and global regulation in bacteria.

Gene expression in bacteria can be regulated at the level of __ control (for example, the lac operon).

Transcriptional

The lac operon comprises the genes lacZ, lacY, and lacA, encoding β-galactosidase, __, and transacetylase.

permease

In the lac operon, the repressor binds the operator when lactose is __.

absent

The actual inducer that reduces repressor binding in the lac operon is __ (the true inducer is allolactose).

allolactose

Catabolite repression of the lac operon occurs when glucose is present, which lowers __ levels and reduces CAP activation.

cAMP

The CAP–cAMP complex activates transcription by helping RNA polymerase bind to the lac promoter at the __ region.

-10/-35 boxes

When glucose is absent, cAMP levels rise and CAP-cAMP enhances lac operon transcription, illustrating __ regulation.

positive

A sigma factor is an RNA polymerase subunit that binds promoter DNA to initiate transcription and is __ after initiation.

released

Most E. coli promoters have two key elements bound by RNA polymerase: the –35 box and the –10 box, separated by about __ base pairs.

17

The –35 box consensus sequence is and the –10 box consensus sequence is .

TNATATT; TATAAT

Cis-acting elements such as Oc act on nearby genetic sequences, whereas trans-acting factors like the lacI repressor can act __ in the cell.

anywhere

Oc mutations cause the lac operon to be __ (constitutively expressed).

always on

lacI- mutations produce defective repressors that cannot bind the operator, so the lac operon is __.

always on

The lacI+ repressor protein can act in __ to repress lac operons; introducing a wild-type lacI on a plasmid demonstrates this trans-acting effect.

trans

The lac operon is expressed only when lactose is present and glucose is __, a phenomenon known as __ repression.

absent; catabolite repression

In the arabinose operon, AraC acts as an activator by binding to the __ region in the presence of arabinose.

araI

In addition to AraC activation, the CAP–cAMP system provides __ control of the arabinose operon transcription.

positive

In the absence of arabinose, AraC binds both araI and araO to form a DNA __ that prevents RNA polymerase from initiating transcription.

loop

Arabinose operon regulation can involve two AraC binding sites at araI; in the absence of arabinose, AraC binds to araO and araI as a dimer to prevent transcription via __.

DNA looping

Global regulation in bacteria can reprogram large gene networks using different __ factors, with sigmas like σ70 recognizing canonical promoters.

sigma

Most bacteria have multiple sigma factors; the housekeeping sigma factor in E. coli that recognizes canonical –35/–10 promoters is __.

sigma70

Consensus sequences describe the most commonly encountered nucleotides at a location across species, determined by comparing sequences via __ alignment.

multiple sequence

The majority-rule consensus for the –35 box is __.

TNATATT

The majority-rule consensus for the –10 box is __.

TATAAT

Optimal spacing between the –35 and –10 regions is important because RNA polymerase contacts both; this spacer length is defined by the spacer’s __.

length

Promoters, operators, and activator sites enable the construction of genetic __ that implement regulatory logic.

circuits