The function of a ribosomal frameshifting signal from human immunodeficiency virus-1 in Escherichia coli

A 15-17 nucleotide sequence from the gag-pol ribosome frameshift site of HIV-1 directs analogous ribosomal frameshifting in Escherichia coli. Limitation for leucine, which is encoded precisely at the frameshift site, dramatically increased the frequency of leftward frameshifting. Limitation for phenylalanine or arginine, which are encoded just before and just after the frameshift, did not significantly affect frameshifting. Protein sequence analysis demonstrated the occurrence of two closely related frameshift mechanisms. In the first, ribosomes appear to bind leucyl-tRNA at the frameshift site and then slip leftward. This is the 'simultaneous slippage' mechanism. In the second, ribosomes appear to slip before binding aminoacyl-tRNA, and then bind phenylalanyl-tRNA, which is encoded in the left-shifted reading frame. This mechanism is identical to the 'overlapping reading' we have demonstrated at other bacterial frameshift sites. The HIV-1 sequence is prone to frame-shifting by both mechanisms in E. coli.