[Effect of the primary structure of RNA on the pulse character of RNA elongation in vitro by Escherichia coli RNA polymerase: a model].

The elongation rate of RNAs synthesized from AI promoters of T7 phage DNA and its deletion mutant delta DIII T7 DNA by E. coli RNA polymerase was analyzed. The distribution of incorporation rates of any definite nucleotides at any definite position along the two RNA chains was studied. The minimal structure which reproducibly forms pauses seems to be trinucleotide. Two main groups of trinucleotides could be distinguished: 1) those mostly associated with pauses and; 2) those usually found in pause free regions. The first group consists of AUG, AUA, AUC, AAU, GUG, GUA, CGU, CGC, UUA, UUU; the second one comprises AAA, CAA, CCC, UCC, CUA, CUG, CUC, GGG, ACU, GAG, GAA, GGA. A model accounting for intermittent elongation has been developed. It is based on the hypothesis that the kinetic constants of each nucleotide incorporation to and pyrophosphorolysis from the 3'-end of the growing RNA chain depend on the nature of the incoming nucleotide as well as on the nature of a nucleotide residue situated at the 3'-end of the growing RNA. A general equation describing the pause distribution along the RNA of a known nucleotide sequence is proposed.