The entire DNA sequence of chromosome III of the yeast Saccharomyces cerevisiae has been determined. This is the first complete sequence analysis of an entire chromosome from any organism. The 315-kilobase sequence reveals 182 open reading frames for proteins longer than 100 amino acids, of which 37 correspond to known genes and 29 more show some similarity to sequences in databases. Of 55 new open reading frames analysed by gene disruption, three are essential genes; of 42 non-essential genes that were tested, 14 show some discernible effect on phenotype and the remaining 28 have no overt function.

The rimI gene of Escherichia coli K12, which encodes an enzyme catalysing acetylation of the N-terminal alanine of ribosomal protein S18, has been cloned into a mini-F plasmid pRE432 and characterized at the molecular level. Similarly, the rimJ gene, which encodes another acetylating enzyme that is specific for ribosomal protein S5, has been cloned and characterized. From the nucleotide sequence data for the two genes the RimI enzyme was deduced to contain 161 amino acid residues with a calculated molecular weight (Mr) of 18232 and the RimJ enzyme contains 194 amino acid residues with a calculated Mr of 22687. The proteins produced from the two genes in maxi-cells were identified by electrophoresis on acrylamide gels and their operon structure was analysed by insertional mutagenesis with transposon gamma delta (Tn1000) and by measuring the size of their transcripts. Their structural homology was analysed by DNA hybridization and by calculation with computer programs. There is only a low level of overall homology between the two genes except for a 3' terminal region in which a significant degree of homology was noticed.

The receptor for granulocyte colony‐stimulating factor (G‐CSFR) is a hemopoietic growth factor receptor, which mediates proliferation and differentiation signals. The cytoplasmic region of G‐CSFR carries four tyrosine residues in its C‐terminal half. We constructed mutant receptors in which each tyrosine residue of G‐CSFR was mutated to phenylalanine. Two mutant receptors (Tyr703 and Tyr728) neither transduced the growth‐inhibitory signal nor induced the neutrophil‐specific myeloperoxidase (MPO) gene. The Tyr703 mutant did not induce morphological changes in cells, whereas transformants expressing the Tyr728 mutant adhered to plates with a macrophage‐like morphology upon G‐CSF stimulation. Mutation of the most distal tyrosine residue (Tyr763) abolished the ability of G‐CSFR to stimulate the tyrosine phosphorylation of a cellular protein with an M(r) of 54 kDa. These results indicated that the regions around the three tyrosine residues of G‐CSFR play essential and distinct roles in signal transduction.

Using lambda phage vector EMBL4, we isolated 344 clones containing segments of chromosome III of Saccharomyces cerevisiae, analysed their physical structure with eight restriction enzymes and sorted the data in contiguous groups with computer programmes. Furthermore, we performed Southern hybridizations between the sorted contiguous clone groups and interrelated them into larger groups. In this way, we constructed an ordered clone bank that covers almost the whole of chromosome III with a single gap of several kilobases in length. The consensus physical map thus obtained totals 334.6 kb, which is in good agreement with the size of this chromosome estimated by pulsed-field gel electrophoresis. Southern hybridization analysis with the DNA probes containing telomere-specific sequences showed that the bank contained a telomere at a position corresponding to the right arm terminus of chromosome III. Also, five Ty elements were found to be present. To estimate the number of genes on this chromosome and to analyse their levels of expression, we performed a series of Northern hybridization experiments using total poly(A)+ RNA from vegetatively growing cells and appropriate restriction enzyme fragments from the bank. Thus, we identified a total of 156 transcripts on chromosome III, indicating, on an average, one gene in every 2 kb on this chromosome. The transcripts were visually categorized into five groups according to their apparent levels of expression. It was found that the genes located near both termini are expressed only at low levels and that highly expressed genes are rather scattered over the chromosome.

The rimL gene of Escherichia coli K12 encodes an enzyme catalyzing the acetylation of the N-terminal serine of ribosomal protein L12, thereby converting it into L7. Using a mutant strain defective in this acetylation reaction, we cloned the rimL gene into cosmid pHC79 and characterized it at the molecular level. From analysis by SDS-polyacrylamide gel electrophoresis of the proteins synthesized in maxi-cells containing derivatives of the rimL-harboring plasmid into which transposon gamma delta had been inserted at various sites, the product of this gene was identified as a protein with an apparent molecular weight of 20.3 kDa. The nucleotide sequence of the gene and the amino acid sequence deduced from the nucleotide sequence were compared with those of two other ribosomal protein acetylases encoded by the rimI and rimJ genes (Yoshikawa et al. 1987). A considerable degree of overall similarity was seen between rimL and rimJ, but the degree of similarity between rimL and rimI was very low. In addition, a short stretch of similar amino acid sequence was found in all three rim acetylases. The significance of these results with respect to other acetylating enzymes, in particular those involved in the acetylation of aminoglycoside antibiotics is discussed.