MATERIALS AND METHODS

Nucleoside triphosphates and 2/-deoxycytidine triphosphate (special quality for molecular biology, 100 mM) were purchased from Boehringer Mannheim.[14C] ATP (specific activity 50mCi/mmol),[a-32P] GTP (specific activity~ 3000 Ci/mmol) and [7-32P] ATP (specific activity> 5000 Ci/mmol) were from Amersham Buchler, Braunschweig, FRG. Liquid scintillant Szintillator 303 was obtained from Riedel-deHaen, Seelze, FRG. The restriction endonuclease RyfNI (10 units/pL) was from New England Biolabs, T4 polynucleotide kinase (30 units/jiL) was purchased from US Biochemicals, and ultrapure calf intestinal alkaline phosphatase (1 unit/jtL) was from Boehringer Mannheim. Plasmid pSPTl 9 was obtained from Pharmacia. Plasmid AspUC 19 containing the gene for Escherichia coli tRNAAsp behind the T7 promoter was a generous gift from D. Schatz (Gottingen, FRG). Plasmid pTFMa containingthe gene for yeast tRNAAsp (Perret et al., 1990) was a kind gift from R. Giege (Strasbourg, France). The plasmids were isolated according to the Qiagen plasmid maxi preparation method provided by Diagen Dusseldorf, FRG. The concentration of plasmid was determined by using