The gene encodingBacillus subtilisUMP kinase (pyrH/ smbA) is transcribed in vivo into a functional enzyme, which represents approximately of total soluble proteins. The specific activity of the purified enzyme under optimal conditions is 25 unitsÆmg )1 of protein. In the absenceofGTP,theactivityofB. subtilisenzyme is less than 10% of its maximum activity. Only dGTP and 3¢-anthraniloyl-2¢-deoxyguanosine-5¢-triphosphate (Ant-dGTP) can increase catalysis significantly.