| Abstract: | The codon that is in-frame prior to +1 frameshifting at the E.coli prfB (RF2 gene) frameshift site is randomized to create thirty-two variants. These alleles vary 1000-fold in frameshift-dependent expression in fusions to lacZ. Frameshifting is more frequent at sites where the in-frame codon ends in uridine, as if third position wobble pairs to message uridine facilitate slippage into the +1 frame. Consistent with other studies of programmed frameshift sites, efficient frameshifting depends on stable message:tRNA base pairs after rephasing. For complexes with mispairs, frameshift frequency depends on the nature, number, and position of mispairs. Central purine:purine mispairs are especially inhibitory. Relative stabilities of +1 rephased complexes are estimated from published data on the stabilities of tRNA:tRNA complexes. Stability correlates with frameshifting over its entire range, which suggests that stability is an important determinant of the probability of translation of the rephased complex. |
