Saccharomyces cerevisiae contains two discrete genes coding for the alpha-factor pheromone.

Two genes, MF alpha 1 and MF alpha 2, coding for the alpha-factor in yeast Saccharomyces cerevisiae were identified by in situ colony hybridization of synthetic probes to a yeast genomic library. The probes were designed on the basis of the known amino acid sequence of the tridecapeptide alpha-pheromone. The nucleotide sequence revealed that the two genes, though similar in their overall structure, differ from each other in several striking ways. MF alpha 1 gene contains 4 copies of the coding sequence for the alpha-factor, which are separated by 24 nucleotides encoding the octapeptide Lys-Arg-Glu-Ala-Glu(or Asp)-Ala-Glu-Ala. The first alpha-factor coding block is preceded by a sequence for the hexapeptide Lys-Arg-Glu-Ala and 83 additional amino acids. MF alpha 2 gene contains coding sequences for two copies of the alpha-factor that differ from each other and from alpha-factor encoded by MF alpha 1 gene by a Gln leads to Asn and a Lys leads to Arg substitution. The first copy of the alpha-factor is preceded by a sequence coding for 87 amino acids which ends with Lys-Arg-Glu-Ala-Val-Ala-Asp-Ala. The coding blocks of the two copies of the pheromone are separated by the sequence for Lys-Arg-Glu-Ala-Asn-Ala-Asp-Ala. Thus, the alpha-factor can be derived from 2 different precursor proteins of 165 and 120 amino acids containing, respectively, 4 and 2 copies of the pheromone.     

D-lysine catabolic pathway in Pseudomonas putida: interrelations with L-lysine catabolism

The isolation of several mutant strains blocked in l-lysine degradation has permitted an assessment of the physiological significance of enzymatic reactions related to lysine metabolism in Pseudomonas putida. Additional studies with intact cells involved labeling of metabolic intermediates from radioactive l- or d-lysine, and patterns of enzyme induction in both wild-type and mutant strains. These studies lead to the conclusions that from l-lysine, the obligatory pathway is via delta-aminovaleramide, delta-aminovalerate, glutaric semialdehyde, and glutarate, and that no alternative pathways from l-lysine exist in our strain. A distinct pathway from d-lysine proceeds via Delta(1)-piperideine-2-carboxylate, l-pipecolate, and Delta(1)-piperideine-6-carboxylate (alpha-aminoadipic semialdehyde). The two pathways are independent in the sense that certain mutants, unable to grow on l-lysine, grow at wild-type rates of d-lysine, utilizing the same intermediates as the wild type, as inferred from labeling studies. This finding implies that lysine racemase in our strain, while detectable in cell extracts, is not physiologically functional in intact cells at a rate that would permit growth of mutants blocked in the l-lysine pathway. Pipecolate oxidase, a d-lysine-related enzyme, is induced by d-lysine and less efficiently by l-lysine. Aminooxyacetate virtually abolishes the inducing activity of l-lysine for this enzyme, suggesting that lysine racemase, although functionally inactive for growth purposes, may still have regulatory significance in permitting cross-induction of d-lysine-related enzymes by l-lysine, and vice versa. This finding suggests a mechanism in bacteria for maintaining regulatory patterns in pathways that may have lost their capacity to support growth. In addition, enzymatic studies are reported which implicate Delta(1)-piperideine-2-carboxylate reductase as an early step in the d-lysine pathway.     

The corrected nucleotide sequence of yeast leucine transfer ribonucleic acid

The nucleotide sequence of “Renaturable” leucine transfer RNA from Baker's yeast has been re-investigated. The results showed that (i) this tRNA has a sequence of DCD at positions 19–21, (ii) it has an anticodon m⁵CAA and (iii) it has a pseudouridine at position 40.