From “Need for Speed: Molecular Ticket Determines RNA’s Destination and Speed Inside Egg Cell” ( ScienceDaily, Mar. 18, 2012), we learn,
— Like any law-abiding train passenger, a molecule called oskar RNA carries a stamped ticket detailing its destination and form of transport, scientists at the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany, have found. They show that for this molecule, moving in the right direction isn’t enough: speed is of the essence. Their study, published online March 18 in Nature Structural & Molecular Biology, also provides clues as to how a single molecule could receive tickets for different destinations, depending on what type of cell it is in.
When they genetically altered the SOLE tag, the scientists found that oskar didn’t go to the oocyte’s posterior pole, as it should. But surprisingly, it did still move, and seemingly in the right direction. The problem, the researchers realised, was that oskar is racing towards a moving target. As the oocyte grows, it becomes longer, in effect taking the posterior pole further and further away as oskar is carried towards it. With a defective SOLE tag, oskar seemed unable to move fast enough to overcome the oocyte’s growth. So somehow this ‘ticket’ affects the speed of transport, too.
Like the difference between first class mail, and third class mail? All a big accident, right?