A carboxyl-terminal cysteine residue is required for palmitic acid binding and biological activity of the ras-related yeast YPT1 protein.

The Saccharomyces cerevisiae YPT1 gene codes for a ras-like, guanine nucleotide-binding protein which is essential for cell viability. The functional significance of two consecutive cysteines at the very carboxyl-terminal end of this protein and in ypt homologues of other eukaryotic species was examined. YPT1 gene mutations were generated that either led to substitutions by serine or the deletion of one or both C-terminal cysteines. The consequences of the mutations were checked in cells after replacing the wild type with the mutant genes. It was found that as long as one of the cysteines was retained, the protein was fully functional. The YPT1 protein could be labelled with [3H]palmitic acid that appeared to be bound in an ester linkage. The wild-type protein was evenly distributed between soluble and membrane-associated proteins, the palmitoylated form was predominantly in the crude membrane fraction. The mutant protein lacking the C-terminal cysteines was not palmitoylated and was exclusively found in the soluble fraction. The extension by three residues, -Val-Leu-Ser, generating a ras-typical C-terminal end, did not interfere with the mutant YPT1 protein's function although it resulted in a reduced labelling with palmitic acid.

Biochemical properties of the ras-related YPT protein in yeast: a mutational analysis.

Using site-directed mutagenesis, the ras-related and essential yeast YPT1 gene was changed to generate proteins with amino acid exchanges within conserved regions. Bacterially produced wild-type proteins were used for biochemical studies in vitro and were found to have properties very similar to mammalian ras proteins. Gene replacement allowed the study of physiological consequences of the mutations in yeast cells. Lys21----Met and Asn121----Ile substitutions rendered the protein incapable of binding GTP and caused lethality. Ser17----Gly and Ala65----Thr substitutions slightly changed the protein's apparent binding capacity for either GDP or GTP and altered its intrinsic GTPase activity. These mutations were without effect on cellular growth. The YPTgly17,thr65 mutant protein displayed a significantly altered relative capacity for guanine nucleotide binding but a GTPase activity comparable to the wild-type protein. In contrast to the Ala65----Thr substitution, the double mutant displayed a significantly reduced capacity for autophosphorylation and allowed cells to grow only poorly. Cellular growth was improved when this mutant protein was overproduced.

Yeast contains two functional genes coding for ribosomal protein S10.

The DNA sequence of the second copy of the gene coding for yeast ribosomal protein S10 was determined and compared with the sequence of the first gene-copy. In addition, the sites at which the transcription of these genes start and terminate are identified. The amino acid coding regions of the two gene copies are virtually identical. The leader and in particular the trailer sequences, however, are significantly different, while the intervening sequences have hardly any homology. Taking advantage of the sequence differences we could establish that both genes are expressed in the vegetatively growing yeast cell; the respective transcripts, however, differ in their relative amounts.

The gene for yeast ribosomal protein S31 contains an intron in the leader sequence.

Analysis of the primary structure of the gene for yeast ribosomal protein S31 revealed two unusual features. First, an intron of 312 nucleotides is located within the 5'-untranslated region. Second, the coding sequence for the known amino-terminal peptide of the protein starts 13 codons downstream of the ATG initiation codon, suggesting that S31 is synthesized as a precursor which undergoes post-translational processing to the mature protein. Primer extension analysis showed that transcription of the S31 gene starts at multiple sites. The 5'-flanking region of the gene contains several, previously described, conserved sequence elements that may play a role in the coordinate expression of yeast ribosomal protein genes.

Structure and organization of two linked ribosomal protein genes in yeast.

The genes encoding yeast ribosomal proteins rp28 and S16A are linked and occur duplicated in the yeast genome. In both gene pairs the genes are approximately 600 bp apart and are both transcribed in the same direction. Both ribosomal protein genes resemble other ribosomal protein genes studied so far in many structural aspects. The genes are interrupted by an intron near the 5'-end of their coding sequence. In addition the flanking regions contain several conserved sequence elements, which may function in transcription initiation and termination. In agreement with findings concerning other cloned yeast ribosomal protein genes, upstream homology blocks occur that may be involved in coordinate control of ribosomal protein gene transcription. The complete pattern of conserved and diverged sequences between the two duplicate gene pairs is presented.

The primary structure of a gene encoding yeast ribosomal protein L34.

Sequence analysis revealed that a gene coding for yeast ribosomal protein L34 comprises an amino acid coding region of 339 nucleotides which is interrupted by an intron after the 19th codon. Like for other yeast ribosomal protein genes analyzed thus far a strong codon bias was observed. The flanking and intervening sequences of this gene encoding L34 show several elements that are conserved in a number of split ribosomal protein genes in yeast. Northern blot analysis using an intron-specific probe demonstrated that the sequenced gene copy coding for L34 is transcribed in vivo.

The structure of the gene coding for the phosphorylated ribosomal protein S10 in yeast.

From previous studies on cloned yeast ribosomal protein genes we obtained evidence that a large number of them contain an intron [Bollen et al. (1982) Gene 18, 29-38]. In the temperature-sensitive rna2-mutant transcription of these genes leads to the accumulation of precursor RNAs at the restrictive temperature. These precursor mRNAs are several hundreds of nucleotides longer than the respective mature mRNAs. The split character of one of these ribosomal protein genes, viz. the gene coding for the major phosphorylated small-subunit protein S10, was further established by sequence analysis. The intervening sequence interrupts the coding sequence after the second codon and has a length of 352 nucleotides. Genomic Southern hybridizations with a DNA fragment carrying part of the S10-gene revealed that this gene is duplicated on the yeast genome. The molecular weight of S10 as deduced from the sequence analysis was estimated to be 31462 dal. Comparison of the N-terminal aminoacid sequence of the yeast ribosomal protein S10 with that of ribosomal protein S6 from rat liver revealed a striking homology between both proteins. Moreover, at the C-terminal end of the yeast ribosomal protein the sequence Arg-Ala-Ser-Ser-Leu-Lys is present which is very similar to the phosphorylation site of the rat liver protein S6.

Ribosomal protein genes of yeast contain intervening sequences.

From a colony bank of HindIII-generated yeast DNA fragments we have isolated a number of recombinant DNAs carrying genes for ribosomal proteins (e.g., S10, S16A, S20, S24, S31, S33, L16, L25 and L34) of the yeast Saccharomyces carlsbergensis. By electron microscopic analysis of the R-loops formed between various DNA fragments and yeast mRNA, we could locate the ribosomal protein genes on the physical maps of the cloned DNA fragments. The R-loop structures observed indicate that a number of the ribosomal protein genes contain an intervening sequence.