Cells' innards may share origin.

Despite their outward differences, many of the organelles within cells may have a common evolutionary heritage.

In a ease of scientific serendipity, data gathered by separate research teams working on various organelles lend new support to the theory that a simpler cellular compartment gave rise to the organelles' diverse modern forms.

"We all had been looking at specific organelles, but sitting there [at the conference] listening to the other scientists speak, there seemed to be something common in all of them,' says Damien Devos of the European Molecular Biology Laboratory in Heidelberg, Germany.

Several research groups had been studying proteins that guide the movements and interactions of organelles such as the Golgi apparatus, the endoplasmic reticulum (ER) and the nucleus.

"The data are contradictory if you look at one protein at a time,' says Joel B. Dacks of the University of Cambridge in England. "But if you look at them together, it fits."

Each protein on an organelle has evolved at a different rate, so each tells a different story about how long ago that organelle might have diverged from an ancient, simpler organelle and begun developing unique functions.

But Dacks suggests that because all the proteins on one organelle must function together, a change in even one protein could be enough to send the whole compartment off in a new evolutionary direction.

Viewed this way, the measured similarities among the versions of organelle proteins such as Rab, SNARE, and Adaptin suggest they all evolved from a compartment in an ancestral cell that lived long before multicellular life arose, Devos and Dacks say. Such a scenario would contradict the idea that organelles such as the Golgi apparatus and the ER independently evolved, perhaps from pockets in the cell's outer membrane.

"They all came from the same place," Dacks postulates. However, even if further research supports the new theory, it would not apply to energy-converting mitochondria or sunlight-absorbing chloroplasts, which are known to have evolved from ancient, independent-living bacteria that became incorporated into the cells.