Two very different components of messenger RNA in an insect cell line.

The messenger RNA lifetimes have been measured in a cell line derived from an invertebrate source, the mosquito Aedes albopictus. The experiments were made possible by a new technique for obtaining undegraded cytoplasmic RNA from cells with high endogenous nuclease levels. There are two components to the decay kinetics of Aedes mRNA. The major fraction of the steady state message population has a half-life of 20 hr which is, as in mammalian cells, comparable to the cell generation time. The short-lived component turns over very rapidly with a half-life estimated to be about 1.2 hr. The difference in lifetime between the short and long-lived components is about 15 fold in these cells, compared to 3-4 fold in mammalian cells. This may reflect the need for a more responsive mRNA regulating system in poikilothermic organisms. The great disparity between the principle messenger lifetimes permits a more definite assignment of a two component behavior to message decay. The data in the case of mammalian cells could not rule out a family of intermediate lifetimes. The long-lived mRNA has a much smaller average sedimentation value than the short-lived material. The effect is similar to, but much larger than, that seen in mammalian cells. Although the lifetime difference is much greater in the insect cells than in human (HeLa) cells, the fast and slow components comprise about the same proportion of the steady state mRNA population: 30 percent and 70 percent, respectively.