The germination mutant TM-31 of Bacillus megaterium ATCC 12872, was isolated by transposon Tn917 insertional mutagenesis. Glucose, L-proline, L-leucine and KNO3 germinated TM-31 poorly. The DNA in the region of the Tn917 insertion was cloned, and its nucleotide sequence determined. One major open reading frame was present on the cloned DNA. The hydrophobic protein encoded is presumably membrane-associated. A homology search revealed that the gene encoded in the region of the Tn917 insertion is homologous to napA of Enterococcus hirae. napA codes for the NaH-antiporter. It is hypothesized that transport of cations must play an important role in spore germination in B. megaterium ATCC 12872.