A new cell for microspectrophotometry and its use in studying tRNA-Leu-CUG from Escherichia coli

tRNA_CUG^Leu is believed not to contain 4-thiouridine, but its absorption spectrum contains a peak at 338 nm of magnitude about 1% of A₂₆₀. This has been verified by carrying out serial dilutions of dissolved crystalline material, using a microspectrophotometer with a new cell requiring only 1.5 μl for a path length of 3 mm. Crystallizable tRNA^Phe and tRNA_GUA.G^Val show normal 4-thiouridine peaks of magnitude 2% of A₂₆₀, so the anomalous spectrum seems unlikely to be an artefact of the isolation procedure used for all three species.