Oh. Martinezcosta et al., THE RELA SPOT-HOMOLOGOUS GENE IN STREPTOMYCES-COELICOLOR ENCODES BOTHRIBOSOME-DEPENDENT (P)PPGPP-SYNTHESIZING AND (P)PPGPP-DEGRADING ACTIVITIES/, Journal of bacteriology, 180(16), 1998, pp. 4123-4132
Streptomyces coelicolor (p)ppGpp synthetase (Rel protein) belongs to t
he RelA and SpoT (RelA/SpoT) family, which is involved in (p)ppGpp met
abolism and the stringent response. The potential functions of the rel
gene have been examined. S. coelicolor Rel has been shown to be ribos
ome associated, and its activity in vitro is ribosome dependent. Analy
sis in vivo of the active recombinant protein in well-defined Escheric
hia coli relA and reLA/spoT mutants provides evidence that S, coelicol
or Rel, like native E. coli RelA, is functionally ribosome associated,
resulting in ribosome-dependent (p)ppGpp accumulation upon amino acid
deprivation. Expression of an S. coelicolor C-terminally deleted Rel,
comprised of only the first 489 amino acids, catalyzes a ribosome-ind
ependent (p)ppGpp formation, in the same manner as the E. coli truncat
ed RelA protein (1 to 455 amino acids). An E. coli relA spoT double de
letion mutant transformed with S. coelicolor rel gene suppresses the p
henotype associated with (p)ppGpp deficiency. However, in such a strai
n, a rel-mediated (p)ppGpp response apparently occurs after glucose de
pletion, but only in the absence of amino acids. Analysis of ppGpp dec
ay in E. coli expressing the S. coelicolor rel gene suggests that it a
lso encodes a (p)ppGpp-degrading activity. By deletion analysis, the c
atalytic domains of S. coelicolor Rel for (p)ppGpp synthesis and degra
dation have been located within its N terminus (amino acids 267 to 453
and 93 to 397, respectively). In addition, E. coli relA in an S. coel
icolor rel deletion mutant restores actinorhodine production and shows
a nearly normal morphological differentiation, as does the wild-type
rel gene, which is in agreement with the proposed role of (p)ppGpp nuc
leotides in antibiotic biosynthesis.