The objectives of this project are: 1) To isolate and amplify genes coding for tRNAs (particularly phenylalanine tRNA) from mouse cells. 2) To determine the nucleotide sequences of transcribed and non transcribed DNA loci in mouse tRNA genes. 3) To isolate tRNA precursors, including the primary transcription products of tRNA genes. 4) To determine the heterogeneity of DNA loci (intervening and flanking regions) associated with the reiterated tRNA coding sequences. 5) To determine the function of non-coding sequences within tRNA genes. 6) To determine whether individual genes coding for tRNAs are expressed differentially during the in vitro differentiation of mouse Friend cells. These will be accomplished by: 1) Preparing a mouse DNA - lambda Charon 4A recombinant library and isolating tRNA genes from it. 2) Sequencing recombinant DNAs containing tRNA genes. 3) Isolating tRNA precursors from pulse-labelled Friend cells using recombinant DNAs as affinity reagents. 4) Comparing the restriction maps and sequences of a number of independently derived clones coding for tRNAs. 5) Examining the transcription of isolated mouse tRNA genes in vitro.