11.   Guarente and his colleagues showed that when the yeast helicase gene is disrupted, the yeast cells become more sensitive to the waste circles and age prematurely.

12.   If two proteins bind to one another, he said, the yeast cell where this happens turns blue.

13.   In a key experiment, they tricked yeast cells into creating DNA circles to see if their presence would lead to signs of aging.

14.   Most cells, including human cells and yeast cells and most other viruses, have a different docking mechanism for carrying out protein synthesis.

15.   The researchers have discovered the aberrant circles in old yeast cells without the premature-aging defect.

16.   To learn what a gene does in yeast cells, molecular biologists simply delete it and watch to see how the cell functions without it.

17.   Yeast cells ordinarily lead lives independent of one another as they leaven bread dough, ferment grape juice or cause yeast infections.

18.   Writing in the journal Molecular Cell, researchers report that increased levels of manganese in yeast cells slow the activity of a key enzyme, reverse transcriptase.

19.   Yeast cells are not the only creatures that routinely cross the boundary between one-celled and multicellular existence.

20.   Yeast cells possess a helicase-making gene with a similar structure to the human gene.