TTG10

Yes. In that last question, I was asking you to think about how regulation of genes reflects function. Cytokines are a class of protein that are highly potent at inducing a response in low concentrations. Having them hanging around for longer than necessary is a problem. The example, interleukins are part of the inflammatory response. Failure in the ability to stop cytokine production is a feature of many inflammatory diseases and cancers.

And finally.

DNA picks up damage over time and in response to insults such as UV light or carcinogens, and can be inherited. Therefore surveillance systems have evolved to identify and deal with mutations. One such system is known as the nonsense-mediated RNA decay (NMD). NMD’s job is to recognise if the mutation causes formation of stop codon early in the gene (a premature termination codon, PTC), and then degrade the mRNA rather than make a truncated protein.

In human genetic diseases caused by a PTC, NMD could be good or bad. If NMD didn’t happen, a shortened version of the protein could be produced. That short protein, could be partially functional and rescue the disease symptoms or it could be dominant negative, and its expression could “poison” the system making systems worse. In diseases where expressing the short protein could be beneficial, drugs could be used to block NMD.

It is hard to generalise whether NMD blocking drugs would help for a specific gene situation. However, as this is the final question, let’s give it a go. For which of the following human disease causing PTC mutations, might a NMD-blocking drug help alleviate symptoms? *In other words, when might expression of a mutant form of a protein be better than producing no protein at all*