A small protein (arrest peptide) encoded upstream of inducible ornithine carboxylase gene (speF) that controls expression of downstream genes (speF and patE) by nascent chain-translational arrest and transcriptional attenuation. In the presence of ornithine a toeprint due to ribosomal arrest can be seen on the speFL transcript. Only L-ornithine (not other tested amino acids) has this effect (PubMed:32094585). It is thought that in the presence of ornithine, ribosomal stalling on speFL prevents binding of Rho transcription termination factor to a downstream rut site allowing transcription of the operon. In the absence of ornithine, ribosomes terminate translation and are recycled, exposing the rut site allowing Rho to bind and prematurely terminate transcription. The presence of a pair of rare Arg codons could slow down translation to prevent polysome accumulation and to expose the rut site to Rho (Probable). Binds ornithine in stalled 70S ribosomes, blocking the upper two-thirds of the exit tunnel. Contacts 23S rRNA and ribosomal proteins L4 and L22. Induced by ornithine; putrescine does not trigger ribosome stalling and so appears to repress expression. Part of the speFL-speF-potE operon. An N-terminal sensor domain binds ornithine already present in the ribosomal exit tunnel; upon ornithine binding the downstream effector domain compacts in the exit tunnel, causing a shift of 23S rRNA U2585 which blocks the action of peptide chain release factor 1 (prfA), causing ribosome stalling. Changing the amino acid sequence by 2 frameshifts with minimal nucleotide changes indicates the peptide sequence, but not mRNA structure is important. Belongs to the speF operon leader peptide family.