Gene for lysine tRNA1 may be a progenitor of the highly repetitive and transcribable sequences present in the salmon genome.

When salmon total DNA was transcribed in a HeLa cell extract, a discrete 6S RNA was found to be synthesized by RNA polymerase III. We isolated several phage clones containing the 6S RNA gene from a salmon genomic library and determined the sequences of two representative clones. The 5' part of the gene showed remarkable sequence homology with the lysine tRNA1 molecule. This homology extended to secondary structures, and the numbers of nucleotides in the stem and loop structures in the 6S RNA were the same as those in lysine tRNA1. Further, the pseudouridylic acid residues synthesized by HeLa pseudouridylate synthase(s) were determined to be at uridine-27 and uridine-55, which are the positions of these modified nucleosides in lysine tRNA1. These results strongly suggest that the lysine tRNA1 gene is a progenitor of the highly repetitive and transcribable sequences in the salmon genome.