Structure and organization of a cluster of sic tRNA genes in the space between tandem ribosomal RNA gene sets in Bacillus subtilis.

Hybridization of Southern blots of EcoRI digests of total Bacillus subtilis DNA with ribosomal RNA and transfer RNA probes provides evidence of highly clustered tRNA and rRNA genes, with several tRNA clusters being located in spaces which span between tandem ribosomal RNA gene sets. Clones containing these tRNA clusters were isolated from a Charon 4A library. One of them, denoted trrnB, was partially sequenced. A cluster of six tRNA genes was found, with anticodon assignments of Asn, Thr, Gly, Arg, Pro, Ala. This cluster is closely flanked on both sides by ribosomal RNA gene sets, which were identified by sequencing upward through the 5 S rRNA gene, across a space, and into the 23 S rRNA gene, and also sequencing downward into the 16 S rRNA gene. The tRNA gene cluster appears to be organized into at least two transcriptional units separated by an attenuator region. These transcriptional units may be components of the flanking ribosomal RNA operons. The putative promoter region of the downstream 16 S rRNA is organized differently from Escherichia coli; it is smaller and seems less complex. This gene organization provides insight into possible mechanisms for coordinate and differential control of transfer and ribosomal RNA gene expression.