Messenger RNA potential and the delay before exponential decay of messages

Potential is a parameter of messenger RNA decay that measures the ability of a message population to continue to initiate complete translations. It can be measured from the start of induction using a specific inhibitor of translation-initiation. With very short inductions it can be seen that the potential of the β-galactosidase message is not lost at a constant exponential rate until a time (delay time) approximately equal to the time required to synthesize the β-galactosidase message. The capacity to make enzyme declines only after the induction lag and its subsequent decay shows a somewhat longer delay; unlike potential, capacity is also affected by the variable rate of ribosome movement. The delays in loss of potential and capacity are consistent with either of two mechanisms: (1) the message must be completed before attack at its starting end, or (2) two or more separate events (or hits) with specific time constants are needed to inactivate. Even at very low growth temperatures, functional decay kinetics are consistent with either mechanism, as is the mass decay of β-galactosidase message at 37 °C. Messages for anthranilate synthetase and galactoside acetyl-transferase do not require two hits to inactivate, but the data cannot determine if there is a delay equal to their synthesis time. Either β-galactosidase message is exceptional and, as opposed to other messages, requires two or more hits to be inactivated, or Escherichia coli messages generally do not commence to decay until they are completed.