Biological Activity of Cross‐Linked Escherichia coli tRNAfMet

A covalent bond between 4‐thiouridine in position 8 and cytidine in position 13 can be quantitatively introduced in Escherichia coli tRNAfMet by irradiation at 335 nm. The cross‐linked tRNAfMet can be acylated and formylated like the unmodified molecule though the rate of acylation is lower. It is bound normally to 70‐S ribosomes by crude initiation factors in the presence of pAUG or T4 mRNA, and can transfer N‐formyl‐methionine to puromycin. Thus, the initiation process does not require any separation of the 4‐thiouridine and cytidine residues.