Insertional mutagenesis has revealed that a 22 kbp segment from the hisA region of the Bacillus subtilis 168 chromosome (310 degrees on the genetic map) contains at least six independent transcription units, all apparently devoted to production of cell envelope components. Genes concerned with synthesis of poly(glycerol phosphate), poly(groP), an essential cell wall polymer in B. subtilis 168, are organized in two divergently transcribed operons denoted tagABC and tagDEF. Nucleotide sequence analysis indicates that three of these six genes encode extremely basic polypeptides. The deduced products of the tagABC operon may be involved in poly(groP) assembly and export, whereas those of the tagDEF operon, which are very hydrophilic, are more likely to be implicated in poly(groP) precursor biosynthesis. The first gene of the tagDEF operon encodes glycerol-3-phosphate cytidylyltransferase (Pooley et al., 1991, Journal of General Microbiology 137, 921-928) and its deduced product has significant homology with cholinephosphate cytidylyltransferase from yeast. There is also substantial homology between the deduced products of tagB in the tagABC operon and tagF in the tagDEF operon.