STRINGENCY AND RELAXATION AMONG THE HALOBACTERIA

Accumulation of stable RNA and production of guanosine polyphosphates (ppGpp and pppGpp) were studied during amino acid starvation in four s pecies of halobacteria. In two of the four species, stable RNA was und er stringent control, whereas one of the remaining two species was rel axed and the other gave an intermediate phenotype. The stringent react ion was reversed by anisomycin, an effect analogous to the chloroamphe nicol-induced reversal of stringency in the eubacteria. During the str ingent response, neither ppGpp nor pppGpp accumulation took place duri ng starvation. In both growing and starved cells a very low basal leve l of the two polyphosphates appeared to be present. In the stringent s pecies the intracellular concentration of GTP did not diminish but act ually increased during the course of the stringent response. These dat a demonstrate that (i) wild-type halobacteria can have either the stri ngent or the relaxed phenotype (all wild-type eubacteria tested have b een shown to be stringent); (ii) stringency in the halobacteria is dep endent on the deaminoacylation of tRNA, as in the eubacteria; and (iii ) in the halobacteria, ppGpp is not an effector of stringent control o ver stable-RNA synthesis.