If DNA is the book of life, messenger RNAs are the photocopies: duplicate segments of code that move between the cell’s interior compartments to the protein-making machinery. In contrast, microRNAs have the opposite role – they attach to larger RNAs and impede their movement, preventing protein production. In cancer, certain ‘bad’ microRNAs are exported from cells to surrounding tissue where they facilitate growth by attracting blood vessels, blocking growth-inhibition messages, and hindering immune surveillance. They also promote secondary tumours by predisposing distant organs to accept break-away cancer cells. Here, researchers studying breast cancer show that tumour-promoting microRNAs are exported in an unusual way: they are not associated with the typical RNA export proteins (dyed red), instead they are in particles containing proteins (in green) which are normally linked to DNA (dyed blue). These abnormal particles are present in blood so may be useful as a diagnostic marker for breast cancer.
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