Ability of modified forms of phenylalanine tRNA to stimulate guanosine pentaphosphate synthesis by the stringent factor-ribosome complex of E. coli

AUTOR(ES)

Ofengand, James

RESUMO

tRNAPhe of E. coli, modified at its 4-thiouridine (4Srd) and 3-(3-amino-3-carboxypropyl)uridine (nbt3Urd) residues, was tested for its ability to induce (p)ppGpp synthesis. The 4Srd residue was derivatized with the p-azido-phenacyl group, cross-linked to Cyd13, and the borohydride reduction product of the cross-link was prepared. The nbt3Urd residue was derivatized with the N-(4-azido-2-nitrophenyl)glycyl group. None of these derivatives had more than a minor effect on the affinity of the tRNA for the stringent factor-ribosome complex, and no effect at all on the maximum velocity of (p)ppGpp synthesis, either at 2 or 82 mM NH4Cl. These two regions of the tRNA which are on opposite faces of the tRNA molecule do not appear to be structurally important for recognition by the stringent factor-ribosome complex. They may provide useful sites, therefore, for the introduction of photoaffinity or fluorescent probes with which to study tRNA-stringent factor recognition.

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