Sequence organization of a cloned tDNA met fragment from Xenopus laevis.

3.18 kb fragments of X. laevis DNA coding for tRNA 1 met have been inserted into a lambda vector via Hind III termini and cloned in E. coli. The organization of one cloned fragment has been analyzed by restriction endonuclease digestion and RNA-DNA hybridization. From the distribution of sites for three enzymes, this fragment appears to be typical of the majority of X. laevis tandem tDNA 1 met repeat units. Evidence is presented to suggest that it contains two genes coding for tRNA 1 met and at least one gene coding for a second as yet unidentified 4S RNA species. The two tRNA 1 met genes are located on the same DNA strand 0.96 and 1.38 kb from one end of the repeat unit. A detailed restriction map for 19 enzymes reveals that the spacers between these genes are not identical, and it provides no indication of short repetitive sequence elements within the spacers.