Synthesis of ribosomal and transfer ribonucleic acids in yeast during a nutritional shift-up.

The growth rate of Saccharomyces cerevisiae was increased by adding a mixture of amino acids to cultures containing proline as the sole nitrogen source. The transition from balanced growth in the basal medium (doubling time 4 h) to balanced growth in the enriched medium (doubling time 2 h) took about 2-5 h. The rate of RNA accumulation increased soon after the enrichment to almost its final value. This increase began after a short lag of 10 to 15 min, therefore synthesis of new RNA polymerase molecules may be required before stable RNA production can increase. The different stable RNA species were not stimulated at different times after the enrichment, but all increased continuosly throughout the transition. The rRNA species accumulated in a co-ordinate fashion at a rate faster than the rate of tRNA accumulation.     

Half molecules of serine-specific transfer ribonucleic acids from yeast

The preparation and analysis of half molecules from tRNA^Ser are described. Two pG-halves were isolated which differed only in the presence or absence of an acetyl group on the cytidylic acid residue at position 12. The CCA-half derived from tRNA₁^Ser was isolated pure, while the CCA-half derived from tRNA₂^Ser was isolated as a mixture with the CCA-half from tRNA₁^Ser from which the terminal CpCpA had been cleaved off.The acceptor activity of the combined complementary half molecules was 90% of the one of intact tRNA^Ser. The Michaelis constant and maximal velocity of amino-acylation were found to be identical for tRNA^Ser and the combined fragments.When half molecules were present at different ratios in aminoacylation studies it was found that one pG-half molecule can mediate the charging of several CCA-half molecules. There are indications that the CCA-half molecule alone can accept some serine. The CCA-half molecule alone can be aminoacylated to a rather high degree in the presence of an excess of tRNA_ox^Ser or tRNA^Ser-a and to a small degree in the presence of tRNA_ox^Ala (yeast) but not at all in the presence of tRNA_ox^Phe or tRNA_ox^Val (E. coli).Combinations of half molecules from tRNA^Ser with the opposite half molecules from tRNA^Phe could not be aminoacylated with Ser or Phe or 15 other amino acids although one of the combinations was well associated according to gel electrophoresis and differential melting curves.     

The circular dichroism of ribosomal ribonucleic acids.

1. The c.d. (circular dichroism) of Drosophila melanogaster rRNA (42% G+C) and of G+C-rich fragments (78% G+C) obtained by partial hydrolysis of rabbit L-rRNA (the largest RNA species isolated from the large subribosomal particle) were measured and found to differ substantially. 2. To interpret these spectra a relation between c.d. of bihelical RNA and % G+C was derived, namely delta epsilonfG = AFG2+bfG+c, where deltaepsilonfG is the c.d. of RNA characterized by a mole fraction, fG, of guanine nucleotides and a, b and c are constants. 3. A frame of reference was established by studying the c.d. of a range of rRNA species, including S-rRNA (the RNA species isolated from the smaller subribosomal particle) and L-rRNA of Escherichia coli. 4. It was found for the rRNA species studied that 0.60+/-0.05 of residues appear to form bihelical secondary structure. 5. A higher helical content, 0.66+/-0.05, was found for the G+C-rich fragment of L-rRNA. The difference in the c.d. of rabbit L-rRNA and of D. melanogaster rRNA is attributable to the dependence of c.d. of the bihelical parts on %G+C. 6. The minimum in c.d. at 295 nm increases with increasing %G+C. The c.d. of rRNA was compared with that of the parent subparticle in this region of the spectrum, where high precision may be attained.     

Multiple isoacceptor forms of several transfer ribonucleic acids in a mutant yeast strain.

By use of reverse phase 5 chromatography, a strain of Saccharomyces cerevisiae (XB 109-5B) has been shown to exhibit multiple isoaccepting forms for several of the transfer ribonucleic acids (tRNAs). This is in contrast with a standard wild-type strain where only one acceptor is found for each tRNA studied. Multiple peaks for tRNATyr, tRNAPhe, tRNASer, and tRNAVal have been detected for strain XB 109-5B. However, the observation of multiple isoacceptors cannot be extended to all tRNAs in this strain since tRNAAsp appears as a single form that is the same as in the wild type. The appearance of multiple peaks was found to depend on the growth conditions of the cells. The tRNA profiles of XB 109-5B that was grown rapidly with vigorous aeration differed the most from profiles of comparably grown wild-type yeast, whereas tRNA from this mutant, grown without shaking or supplementary aeration, appeared the same as the wild type. The minor nucleoside composition of the isoacceptors of tRNAPhe was obtained.     

Columns for rapid chromatographic separation of small amounts of tracer-labeled transfer ribonucleic acids

A small reversed-phase chromatographic system for the separation of [³H] or [¹⁴C] aminoacyl-tRNA's is described. This system has the advantages of speed (chromatographic runs can be completed in 30 to 60 min), sensitivity (samples containing as little as 3.5 × 10⁻⁹ gm or 60 × 16⁻⁶A₂₆₀ unit of phenylalanyl-tRNA have been resolved as a chromatographic peak), and excellent resolution of isoaccepting tRNA's. The system has been applied to samples of E. coli tRNA's and calf liver tRNA's.