Gene organization and transcriptional analysis of the Spiroplasma citri rpsB/tsf/x operon

The nucleotide sequence of a 6863-bp Spiroplasma citri DNA fragment comprising the spiralin gene was determined. Sequence analysis revealed eight putative ORFs that encode ribosomal protein S2, elongation factor Ts, spiralin, 6-phosphofructokinase, pyruvate kinase, and three unidentified proteins (A, B, and X). The gene organization reported here is different from that previously published. Northern blot analysis of rpsB, tsf, and x transcripts indicates that these genes are organized into a single transcriptional unit (operon). However, the detection of an additional transcript corresponding to the rpsB gene alone suggests that a transcriptional mechanism should occur in the 3' region of the rpsB gene, allowing a conditional transcription termination.