Structural analysis of the tRNA1Tyr gene of Escherichia coli. A 178 base pair sequence that is repeated 3.14 times.

The distal region of the tRNA1Tyr gene has been sequenced and found to have an unusual structure. It consists of a 178 base pair sequence that is repeated 3.14 times. The first repeat unit commences 19 base pairs before the end of the sequences encoding the mature tRNA, and these 19 base pairs are repeated faithfully at the beginning of each repeat unit. In the last fractional unit the repeated sequence extends only six base pairs beyond this 19 base pair sequence. Sequence information extends for 62 base pairs beyond the 3.14 repeating units, and no resemblance to the repeating sequence, or any other region of the tRNA1Tyr gene, is found. There are only 14 sites at which one of the repeats differs from the others; 11 of these are transitions, and the rest are transversions. The evolutionary implications of the differences are discussed. One of the differences, which occurs in the second repeat unit, corresponds to the location of the in vitro p-dependent transcription termination site. This is discussed along with other implications of the repeated structure.