Richter D, Erdmann V A, Sprinzl M
Proc Natl Acad Sci U S A. 1974 Aug;71(8):3226-9. doi: 10.1073/pnas.71.8.3226.
The tetranucleotide TpPsipCpGp, when bound to Escherichia coli 50S ribosomal subunits, can replace intact tRNA in the stringent factor-directed synthesis of guanosine tetra- and pentaphosphates. The TpPsipCpGp-dependent fragment reaction has a strict requirement for the 50S and 30S ribosomal subunits and synthetic or natural messenger RNA.