Anomalies in the guanosine polyphosphate metabolism: Effect of the hisU mutation☆

The hisU1820 mutant (TA799) of Salmonella, typhimurium shows a substantial increase in the levels of ppGpp (MSI) and of pppGpp (MSII) during several types of metabolic shifts. Noticeable amounts of ppGp (MSIII) are also present post-carbon/energy source downshifts and temperature up-shifts. The increased levels of these guanosine polyphosphates were observed despite the absence of the expected reduction in RNA synthesis upon a nutritional downshift. We, therefore, suggest that the hisU mutation causes an increase in the accumulation of MSI and MSII; and that ppGpp alone is not sufficient to promote restriction of RNA synthesis during a nutritional transition.