Chimeric plasmids were constructed such that the cloned complete satellite tobacco necrosis virus (STNV) RNA information came under transcriptional control of the leftward promoter (PL) of bacteriophage lambda. The promoter is fully repressed at low temperatures (28 degrees) by the thermolabile repressor product of the lambdacI857 gene, present in the bacterium on a deficient prophage or as part of another plasmid. Synthesis of the STNV coat protein in Escherichia coli could be initiated by heat induction (42 degrees). These in vivo results confirm that the 5'-untranslated region of STNV RNA, preceding the initiating AUG, provides adequate genetic information for efficient translation in the bacterial system. However, fast degradation of the bacterially synthesized STNV coat protein was observed. The use of a protease-deficient strain reduced this breakdown considerably.