Have you wondered why it’s taking so long to figure out bad, complex diseases like cancer? Well one reason is that basic biological processes–gene regulation in this case–are not as simple as we figured. Ever since they finished sequencing the human genome a few years ago and we learned that we have maybe 25,000 genes instead of the 100,000 we expected, we’ve been discovering that there are additional gene regulation mechanisms that make the 25K genes act like 100K. The latest: micoRNA. From an article in Cell.

For many years, DNA and proteins have been viewed as the real movers
and shakers in genomic studies, with RNA seen as little more than a
messenger that shuttles information between the two. But researchers
from Whitehead Institute for Biomedical Research and Massachusetts
Institute of Technology have discovered that small RNA molecules called
microRNAs regulate thousands of human genes–more than one third of the
genome’s protein-coding regions. In other words, a class of molecule
once relegated to the sidelines may be one of the principal players in
regulating cellular mechanisms.

"As more genome data becomes available and the technology becomes
more sophisticated, I think we’ll find that even more genes are
targeted by microRNAs," predicts Lewis.

In addition, the team discovered some hints about how microRNAs find their targets.

To produce a protein, the cell first makes a template for that protein
by constructing a molecule called messenger RNA. MicroRNAs inhibit
protein production by associating themselves with particular messenger
RNAs, thereby reducing the amount of protein that’s ultimately
produced. In this study, the researchers determined which portion of
the microRNA is most important for this process, and identified
additional determinants in the messenger RNA that are likely to
contribute to recognition by microRNAs.

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