Organization and expression of a two-gene cluster in the arginine biosynthesis of Saccharomyces cerevisiae.

Summary Using the pMB9 recombinant plasmid pMY3, which contains a functional gene for the tRNA^Try mutant Su⁺7, the EcoRI fragment containing the tRNA^Try gene is mapped and oriented with respect to the HindIII site in the tetracycline region of pMB9. Complete HpaII and HaeIII maps of the EcoRI fragment are derived. The Su⁺7 tRNA gene is placed by hybridization to these fragments, and the tRNA gene is oriented by using the restriction sites for HinfI, TaqI, and HpaII in the tRNA gene itself. A tRNA^Asp gene is shown to lie adjacent to tRNA^Try, and is also placed and oriented in the map. The RI fragment itself originates in a locus adjacent to, and transcribed in the same direction as, the ribosomal RNA genes of 80d₃.The implications of the structure of the cloned DNA for its previously measured regulatory and tRNA gene activities are discussed. In particular, the effect on the regulation of RNA synthesis is attributable to an E. coli DNA sequence, but cannot be due to the presence of a normal tRNA promoter on the plasmid.Abbreviations MD megadaltons; expressions of the form HpaII:0.075 refer to a fragment generated by the indicated restriction nuclease, having the indicated molecular weight, in MD