The region of comprises a tricistronic operon, encoding enzymes that catalyse the late stages of menaquinone biosynthesis. The mutation is responsible for a severe growth defect; unsuppressed mutant cells grow as very short rods, which sometimes septate aberrantly. Cultures grow only to a low cell density, rapidly lose viability, and never sporulate. Unlinked suppressor mutations can restore near-normal growth. Several independent suppressed isolates were examined; all grew to normal cell length, but they showed, to varying extents, a residual defect in the placement of the cell division septum. The germination properties of the suppressed derivatives varied from normal to significantly slow in germination in all germinants; therefore, the combination of the mutation and different suppressor alleles resulted in spores with very different germination properties. This suggests that any relationship between the gene products and spore germination is indirect. The mutation maps in a gene encoding the catalytic subunit of the heptaprenyl-diphosphate synthase, which is responsible for formation of the isoprenoid side chain of menaquinone-7, and it is proposed that the and genes be renamed and , respectively.


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