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04:04Neelaredoxin is a 15-kDa protein that is a gene product common in anaerobic bacteria. It has superoxide-scavenging activity, and it is constitutively expressed. In addition, its expression is not further induced during its exposure to O₂ or H₂O₂ [Silva, G. et al. (2001). J. Bacteriol. 183:4413 4420]. What do the terms constitutively expressed and induced mean in terms of neelaredoxin synthesis?
The creation of milk products such as cheeses and yogurts is dependent on the conversion by various anaerobic bacteria, including several Lactobacillus species, of lactose to glucose and galactose, ultimately producing lactic acid. These conversions are dependent on both permease and β-galactosidase as part of the lac operon. After selection for rapid fermentation for the production of yogurt, one Lactobacillus subspecies lost its ability to regulate lac operon expression [Lapierre, L., et al. (2002). J. Bacteriol. 184:928–935]. Would you consider it likely that in this subspecies the lac operon is on or off? What genetic events would likely contribute to the loss of regulation as described above?
During the reproductive cycle of a temperate bacteriophage, the viral DNA inserts into the bacterial chromosome, where the resultant prophage behaves much like a Trojan horse. It can remain quiescent, or it can become lytic and initiate a burst of progeny viruses. Several operons maintain the prophage state by interacting with a repressor that keeps the lytic cycle in check. Insults (ultraviolet light, for example) to the bacterial cell lead to a partial breakdown of the repressor, which in turn causes the production of enzymes involved in the lytic cycle. As stated in this simple form, would you consider this system of regulation to be operating under positive or negative control?
Bacterial strategies to evade natural or human-imposed antibiotics are varied and include membrane-bound efflux pumps that export antibiotics from the cell. A review of efflux pumps [Grkovic, S., et al. (2002)] states that, because energy is required to drive the pumps, activating them in the absence of the antibiotic has a selective disadvantage. The review also states that a given antibiotic may play a role in the regulation of efflux by interacting with either an activator protein or a repressor protein, depending on the system involved. How might such systems be categorized in terms of negative control (inducible or repressible) or positive control (inducible or repressible)?
In a theoretical operon, genes A, B, C, and D represent the repressor gene, the promoter sequence, the operator gene, and the structural gene, but not necessarily in the order named. This operon is concerned with the metabolism of a theoretical molecule (tm). From the data provided in the accompanying table, first decide whether the operon is inducible or repressible. Then assign A, B, C, and D to the four parts of the operon. Explain your rationale. (AE=active enzyme; IE=inactive enzyme; NE=no enzyme.) Genotype tm Present tm Absent A⁺B⁺C⁺D⁺ AE NE A⁻B⁺C⁺D⁺ AE AE A⁺B⁻C⁺D⁺ NE NE A⁺B⁺C⁻D⁺ IE NE A⁺B⁺C⁺D⁻ AE AE A⁻B⁺C⁺D⁺/F'A⁺B⁺C⁺D⁺ AE AE A⁺B⁻C⁺D⁺/F'A⁺B⁺C⁺D⁺ AE NE A⁺B⁺C⁻D⁺/F'A⁺B⁺C⁺D⁺ AE+IE NE A⁺B⁺C⁺D⁻/F'A⁺B⁺C⁺D⁺ AE NE
