Transducing phage lambdarifd18 carries on rRNA transcription unit containing genes for 5S, 16S, and 23S rNAs and also tRNAGlu/2. Mutants were isolated from this phage that carry deletions removing various amounts of the distal end of this transcription unit. These deletions were physically mapped on the lambdarifd18 phage genome. Synthesis of rRNAs and of tRNAGlu/2 was examined in ultraviolet-irradiated E. coli cells infected with lambdarifd18 or with various deletion mutants. It was observed that mutant phages in which the distal end (the 5S rRNA gene and a part of the 23S rRNA gene) of the rRNA transcription unit is deleted can still synthesize both 16S rRNA (or its precursor) and tRNAGlu/2. Apparently, the post-transcriptional cleavage that produces these RNA molecules does not require the presence of the entire transcription unit, that is, it can take place without the complete structure of the transcript ("30S pre-ribosomal RNA"). In addition, the experimental results support the gene order, 16S rRNAGlu/2, 23S rRNA, and 5S rRNA genes, in the rRNA transcription unit carried by lambdarifd18.