Northern blot analysis of RNA from exponentially growing B. mycoides SIN and DX. SIN and DX total RNA was electrophoresed in formaldehyde-agarose and blotted. The same filter was hybridized first to ftsZ and, after stripping, to ftsA DNA probes. The position of ribosomal 23S (2907 bases) and 16S (1530 bases) RNA on the filter is indicated. FtsZ and ftsA RNAs in the band below 16S rRNA are monogenic transcripts. The band below the position of the 23 S rRNA contains the ftsA-ftsZ bigenic transcripts. The transcripts of the genes ftsQ-ftsA-ftsZ are within the uppermost bands together with the transcripts murB-ftsQ-ftsA, detected only by the ftsA probe.