Figure 1.

Conserved patterns are only present in the upstream sequences of plant tRNA genes. The best frequency ‘word’ search was performed in the 5′-region (positions −100 to −9 nt) upstream of the initial nucleotide of the mature nuclear-encoded tRNAs of different organisms allowing none (A) or one mismatch (B) (for details see ‘Materials and Methods’ section). The occurrence of the most frequent six-letter ‘word’ at each position (x-axis) is plotted on the y-axis. Position 0 corresponds by the first nucleotide of the mature tRNA. The six-letter ‘word’ with the highest frequency (highest peak) is indicated above the corresponding peak. The CAA-motifs immediately upstream of the 5′-initial nucleotide of the mature tRNAs are also depicted. The dashed line represents the average frequency value obtained from randomized sequences. The shadowed area indicates the area between the maximum and minimum frequency values derived from the randomized data set. nt, nucleotide.