Messenger RNAs were prepared by in vitro transcription. Plasmid pGENE32 is pUC118 containing a region of phage T4 gene 32 (40) from nucleotide position -54 to +84 (where +1 is the translational start) downstream of an engineered T7 promoter sequence. The introduction of slippery sequence in pGENE32 was performed by sitedirected mutagenesis kit (Stratagene). Transcripts with stem-loop were obtained by in vitro transcription of synthetic genes flanked upstream by T7 RNA polymerase promoter region and downstream by a BamHI restriction site. The synthetic genes were constructed by shotgun ligation of 10 DNA fragments (24-30-mers) covering both strands and ligated in the KpnI and BamHI sites of pGENE32. All transcripts have been purified by denaturing PAGE.