[Demonstration of a sudden change in the use of codons in the vicinity of transcription termination].

A characteristic profile of fluctuations in the use of codons is seen in bacteriophages, Mammal mitochondria and animal viruses. Following DNA in the direction of transcription, one goes slowly from an area rich in codons ending by C to an area rich in codons ending by T and then one falls abruptly in an area rich in C. The termination of transcription is located in the area where the use of codons changes suddenly. It seems that the choice of codons ending by T or C is directed by the necessity to have a variation in the stability of the DNA. We propose a dynamic model where large scale variations of the stability of the DNA regulates the speed of propagation of the RNA-polymerase.