In the beginning of lacZ, $200 nt into the open reading frame, there is a site, called 'pt' in Figure 4A , where the RNA polymerase is caused to terminate if there is inefficient translation initiation of the lacZ gene (38) . In the 0 construct there is no pseudoknot to stimulate frameshift at the slippery site. Therefore, virtually no ribosomes were expected to follow the RNA polymerase from gene 10 into the lacZ part of our gene fusion. As expected, Figure 4B and C, lane '0' shows a prominent band ('SP' for stop polymerase) corresponding in size and probe-ability to this premature termination product. Also, corresponding low amounts of high molecular weight transcripts are detected for this construct. All the other constructs shown in Figure 4 contained frameshift stimulating pseudoknots and a inspection of the northern blot showed that the 'SP' bands probed with both gene10 and lacZ5 0 sequences were present in sizes which correspond to the sizes of the pseudoknots inserted.