Efficacy and safety of switching from basal insulin to sitagliptin in Japanese type 2 diabetes patients.

Basal-supported oral therapy (BOT) is often used to treat poorly controlled type 2 diabetes. However, patients sometimes experience nocturnal and early morning hypoglycemia. Thus, maintaining targeted glycemic control by BOT is limited in some patients. We assessed the efficacy and safety of replacing basal insulin by sitagliptin therapy in Japanese type 2 diabetes patients on BOT. Forty-nine subjects were sequentially recruited for the 52-week, prospective, single arm study. Patients on BOT therapy were switched from basal insulin to sitagliptin. The primary endpoint was change in HbA1c in 52 weeks. The secondary endpoints were dropout rate, changes in body weight, frequency of hypoglycemia, and relationship between change in HbA1c and insulin secretion capacity evaluated by glucagon loading test. The average dose of basal insulin was 15.0±8.4 units. Sixteen subjects (31.3%) were dropped because replacement by sitagliptin was less effective for glycemic control. In these subjects, diabetes duration was longer, FPG and HbA1c at baseline were higher, and insulin secretion capacity was lower. Change in HbA1c in 52 weeks was - 4 mmol/mol (95% CI - 5 to - 4 mmol/mol) (p<0.05). Change in body weight was - 0.71 kg (95% CI - 1.42 to - 0.004 kg) (p<0.05). Frequency of hypoglycemia was decreased from 1.21±1.05 to 0.06±0.24 times/month. HbA1c level was improved if C-peptide index (CPI) was over 1.19. In conclusion, basal insulin in BOT can be replaced by sitagliptin with a decrease in HbA1c level and frequency of hypoglycemia in cases where insulin secretion capacity was sufficiently preserved.

Subband structure of a two-dimensional electron gas formed at the polar surface of the strong spin-orbit perovskite KTaO3.

We demonstrate the formation of a two-dimensional electron gas (2DEG) at the (100) surface of the 5d transition-metal oxide KTaO3. From angle-resolved photoemission, we find that quantum confinement lifts the orbital degeneracy of the bulk band structure and leads to a 2DEG composed of ladders of subband states of both light and heavy carriers. Despite the strong spin-orbit coupling, our measurements provide a direct upper bound for the potential Rashba spin splitting of only Δk(parallel)}~0.02 Å(-1) at the Fermi level. The polar nature of the KTaO3(100) surface appears to help mediate the formation of the 2DEG as compared to nonpolar SrTiO3(100).

Sitagliptin add-on to low dosage sulphonylureas: efficacy and safety of combination therapy on glycaemic control and insulin secretion capacity in type 2 diabetes.

AIMS: To assess the efficacy and safety of combination therapy with sitagliptin and low dosage sulphonylureas on glycaemic control and insulin secretion capacity in Japanese type 2 diabetes. METHODS: Eighty-two subjects were sequentially recruited for the 52-week, prospective, single arm study. Sitagliptin was added on to sulphonylureas (glimepride or gliclazide) with or without metformin. The primary endpoint was a change in A1C. The secondary endpoints were changes in BMI, insulin secretion capacity, blood pressure and urinary albumin excretion, unresponsive rate, and hypoglycaemia. Insulin secretion capacity was evaluated by glucagon loading test. RESULTS: Change in A1C was -0.80% (95% CI -0.90 to -0.68) (p < 0.001). Change in BMI, systemic and diastolic blood pressure, and urinary albumin excretion were -0.38 kg/m(2) (95% CI -0.72 to -0.04) (p < 0.05), -6.7/-3.6 mmHg (95% CI -10.0 to -3.4/-4.8 to -2.4) (p < 0.001), and -43.2 mg/gCr (95% CI -65.7 to -20.8) (p < 0.001) respectively. Mild hypoglycaemia was observed in three cases. The unresponsive rate was 6.1%. Glucagon loading test showed that 0-min and 6-min CPR at baseline and 52-week were not significantly changed: 0-min CPR, 1.58 ± 0.58-1.71 ± 0.73 ng/ml; 6-min CPR, 3.48 ± 1.47-3.58 ± 1.21 ng/ml. Insulin secretion capacity, CPI and SUIT index at baseline did not predict the efficacy of the combination therapy. The final dosages of glimepiride and gliclazide were 1.44 ± 0.90 mg and 34.5 ± 15.3 mg respectively. The dosage of sitagliptin was increased from 50 mg to 69.0 ± 24.5 mg in 52-week. CONCLUSIONS: The combination therapy with sitagliptin and low dosage sulphonylureas was safe and effective for glycaemic control. Glucagon loading test indicated that 1 year administration of sitagliptin and sulphonylureas preserved insulin secretion capacity.

Exendin-4 protects pancreatic beta cells from the cytotoxic effect of rapamycin by inhibiting JNK and p38 phosphorylation.

It has been reported that the immunosuppressant rapamycin decreases the viability of pancreatic beta cells. In contrast, exendin-4, an analogue of glucagon-like peptide-1, has been found to inhibit beta cell death and to increase beta cell mass. We investigated the effects of exendin-4 on the cytotoxic effect of rapamycin in beta cells. Incubation with 10 nM rapamycin induced cell death in 12 h in murine beta cell line MIN6 cells and Wistar rat islets, but not when coincubated with 10 nM exendin-4. Rapamycin was found to increase phosphorylation of c-Jun amino-terminal kinase (JNK) and p38 in 30 minutes in MIN6 cells and Wistar rat islets while exendin-4 decreased their phosphorylation. Akt and extracellular signal-regulated kinase (ERK) were not involved in the cytoprotective effect of exendin-4. These results indicate that exendin-4 may exert its protective effect against rapamycin-induced cell death in pancreatic beta cells by inhibiting JNK and p38 signaling.

Dominant mobility modulation by the electric field effect at the LaAlO3/SrTiO3 interface.

Caviglia et al. [Nature (London) 456, 624 (2008)] have found that the superconducting LaAlO3/SrTiO3 interface can be gate modulated. A central issue is to determine the principal effect of the applied electric field. Using magnetotransport studies of a gated structure, we find that the mobility variation is almost 5 times that of the sheet carrier density. Furthermore, superconductivity can be suppressed at both positive and negative gate bias. These results indicate that the relative disorder strength strongly increases across the superconductor-insulator transition.

Genome-wide identification of genes involved in tolerance to various environmental stresses in Saccharomyces cerevisiae.

During fermentation, yeast cells are exposed to a number of stresses -- such as high alcohol concentration, high osmotic pressure, and temperature fluctuation - so some overlap of mechanisms involved in the response to these stresses has been suggested. To identify the genes required for tolerance to alcohol (ethanol, methanol, and 1-propanol), heat, osmotic stress, and oxidative stress, we performed genome-wide screening by using 4828 yeast deletion mutants. Our screens identified 95, 54, 125, 178, 42, and 30 deletion mutants sensitive to ethanol, methanol, 1-propanol, heat, NaCl, and H2O2, respectively. These deleted genes were then classified based on their cellular functions, and cross-sensitivities between stresses were determined. A large number of genes involved in vacuolar H(+)-ATPase (V-ATPase) function, cytoskeleton biogenesis, and cell wall integrity, were required for tolerance to alcohol, suggesting their protective role against alcohol stress. Our results revealed a partial overlap between genes required for alcohol tolerance and those required for thermotolerance. Genes involved in cell wall integrity and the actin cytoskeleton are required for both alcohol tolerance and thermotolerance, whereas the RNA polymerase II mediator complex seems to be specific to heat tolerance. However, no significant overlap of genes required for osmotic stress and oxidative stress with those required for other stresses was observed. Interestingly, although mitochondrial function is likely involved in tolerance to several stresses, it was found to be less important for thermotolerance. The genes identified in this study should be helpful for future research into the molecular mechanisms of stress response.

Function of the ste signal transduction pathway for mating pheromones sustains MAT alpha 1 transcription in Saccharomyces cerevisiae.

Sterile mutants of Saccharomyces cerevisiae were isolated from alpha * cells having the a/alpha aar1-6 genotype (exhibiting alpha mating ability and weak a mating ability as a result of a defect in a1-alpha 2 repression). Among these sterile mutants, we found two ste5 mutants together with putative ste7, ste11, and ste12 mutants of the signal transduction pathway of mating pheromones. The amino acid sequence of the Ste5p protein predicted from the nucleotide sequence of a cloned STE5 DNA has a domain rich in acidic amino acids close to its C terminus, a cysteine-rich sequence, resembling part of a zinc finger structure, in its N-terminal half, and a possible target site of cyclic AMP-dependent protein kinase at its C terminus. Northern (RNA) blot analysis revealed that STE5 transcription is under a1-alpha 2-Aar1p repression. The MAT alpha 1 cistron has a single copy of the pheromone response element in its 5' upstream region, and its basal level of transcription was reduced in these ste mutant cells. However, expression of the MAT alpha 1 cistron was not enhanced appreciably by pheromone signals. One of the ste5 mutant alleles conferred a sterile phenotype to a/alpha aar1-6 cells but a mating ability to MATa cells.

AAR2, a gene for splicing pre-mRNA of the MATa1 cistron in cell type control of Saccharomyces cerevisiae.

We have isolated a class of mutants, aar2, showing the alpha mating type due to a defect in a1-alpha 2 repression but with alpha 2 repression activity from a nonmater strain of Saccharomyces cerevisiae expressing both a and alpha mating-type information in duplicate. Cells of the aar2 mutant and the aar2 disruptant also show a growth defect. A DNA fragment complementing the aar2 mutation contains an open reading frame consisting of 355 amino acid codons. Northern hybridization showed that cells of the aar2 mutant and disruptant contained alpha 1 and alpha 2 transcripts of the MAT alpha gene (or HML alpha in sir3 cells), but their a1 transcript of MATa (or HMRa in sir3 cells) migrated more slowly than that of the wild-type cells on gel electrophoresis and gave a diffused band. Primer extension analysis showed that the aar2 mutant and disruptant have a defect in splicing two short introns of the a1 pre-mRNA but not in splicing pre-mRNA of ACT1. The alpha mating type, but not the slow-growing phenotype, of the aar2 mutant was suppressed by introduction of an intronless MATa1 DNA. Thus, the AAR2 gene is involved in splicing pre-mRNA of the a1 cistron and other genes that are important for cell growth. The AAR2 locus was mapped on chromosome II beside the SSA3 locus, with a 276-bp space, but was not allelic to either PRP5 or PRP6, which are both located on chromosome II and function in splicing pre-mRNA of ACT1.

AAR1/TUP1 protein, with a structure similar to that of the beta subunit of G proteins, is required for a1-alpha 2 and alpha 2 repression in cell type control of Saccharomyces cerevisiae.

We have cloned a DNA fragment complementing the aar1 mutation defective in the a1-alpha 2 repression of the alpha 1 cistron and haploid-specific genes in Saccharomyces cerevisiae. Nucleotide sequence and mapping data indicated that the AAR1 gene is identical with TUP1, which is allelic to the SFL2, FLK1, CYC9, UMR7, AMM1, and AER2 genes, whose mutations are known to confer a variety of phenotypes, such as thymidine uptake, flocculation, insensitivity to glucose repression, a defect in UV-induced mutagenesis, and a defect in ARS plasmid maintenance. The TUP1/AER2 protein is known to have significant similarity with the beta subunits of G proteins in the C-terminal half, in two glutamine-rich domains in the N-terminal half, and in a central region rich in serine and threonine residues. Disruption of the chromosomal AAR1 gene in alpha and a/alpha cells conferred the nonmating phenotype, and the a/alpha diploids could not sporulate. The AAR1/TUP1 gene is transcribed into a 2.5-kb mRNA independently of the mating-type information of the cell. These observations and mRNA analysis of cell-type-specific genes indicated that the AAR1/TUP1 protein is also indispensable for a1-alpha 2 repression of RME1 and for alpha 2 repression of a-specific genes.

Multiple GCD genes required for repression of GCN4, a transcriptional activator of amino acid biosynthetic genes in Saccharomyces cerevisiae.

GCN4 encodes a positive regulator of multiple unlinked genes encoding amino acid biosynthetic enzymes in Saccharomyces cerevisiae. Expression of GCN4 is coupled to amino acid availability by a control mechanism involving GCD1 as a negative effector and GCN1, GCN2, and GCN3 as positive effectors of GCN4 expression. We used reversion of a gcn2 gcn3 double mutation to isolate new alleles of GCD1 and mutations in four additional GCD genes which we designate GCD10, GCD11, GCD12, and GCD13. All of the mutations lead to constitutive derepression of HIS4 transcription in the absence of the GCN2+ and GCN3+ alleles. By contrast, the gcd mutations require the wild-type GCN4 allele for their derepressing effect, suggesting that each acts by influencing the level of GCN4 activity in the cell. Consistent with this interpretation, mutations in each GCD gene lead to constitutive derepression of a GCN4::lacZ gene fusion. Thus, at least five gene products are required to maintain the normal repressed level of GCN4 expression in nonstarvation conditions. Interestingly, the gcd mutations are pleiotropic and also affect growth rate in nonstarvation conditions. In addition, certain alleles lead to a loss of M double-stranded RNA required for the killer phenotype. This pleiotropy suggests that the GCD gene products contribute to an essential cellular function, in addition to, or in conjunction with, their role in GCN4 regulation.

Putative GTP-binding protein, Gtr1, associated with the function of the Pho84 inorganic phosphate transporter in Saccharomyces cerevisiae.

We have found an open reading frame which is 1.1 kb upstream of PHO84 (which encodes a Pi transporter) and is transcribed from the opposite strand. In Saccharomyces cerevisiae, this gene is distal to the TUB3 locus on the left arm of chromosome XIII and is named GTR1. GTR1 encodes a protein consisting of 310 amino acid residues containing, in its N-terminal region, the characteristic tripartite consensus elements for binding GTP conserved in GTP-binding proteins, except for histidine in place of a widely conserved aspargine residue in element III. Disruption of the GTR1 gene resulted in slow growth at 30 degrees C and no growth at 15 degrees C; other phenotypes resembled those of pho84 mutants and included constitutive synthesis of repressible acid phosphatase, reduced Pi transport activity, and resistance to arsenate. The latter phenotypes were shown to be due to a defect in Pi uptake, and the Gtr1 protein was found to be functionally associated with the Pho84 Pi transporter. Recombination between chromosome V (at the URA3 locus) and chromosome XIII (in the GTR1-PHO84-TUB3 region) by using a plasmid-encoded site-specific recombination system indicated that the order of these genes was telomere-TUB3-PHO84-GTR1-CENXIII.

Transformation of protoplasted yeast cells is directly associated with cell fusion.

The frequency of cell fusion during transformation of yeast protoplasts with various yeast plasmids with a chromosome replicon (YRp or YCp) or 2 mu DNA (YEp) was estimated by two methods. In one method, a mixture of protoplasts of two haploid strains with identical mating type and complementary auxotrophic nuclear markers with or without cytoplasmic markers was transformed. When the number of various phenotypic classes of transformants for the nuclear markers was analyzed by equations derived from binominal distribution theory, the frequency of nuclear fusion among the transformants was 42 to 100% in transformations with the YRp or YCp plasmids and 28 to 39% with the YEp plasmids. In another method, a haploid bearing the sir mutation, which allows a diploid (or polyploid) homozygous for the MAT (mating type) locus to sporulate by the expression of the silent mating-type loci HML and HMR, was transformed with the plasmids. Sporulation ability was found in 43 to 95% of the transformants with the YRp or YCp plasmids, and 26 to 31% of the YEp transformants. When cytoplasmic mixing was included with the nuclear fusion, 96 to 100% of the transformants were found to be cell fusants. Based upon these observations, we concluded that transformation of yeast protoplasts is directly associated with cell fusion.

The PHO84 gene of Saccharomyces cerevisiae encodes an inorganic phosphate transporter.

The PHO84 gene specifies Pi-transport in Saccharomyces cerevisiae. A DNA fragment bearing the PHO84 gene was cloned by its ability to complement constitutive synthesis of repressible acid phosphatase of pho84 mutant cells. Its nucleotide sequence predicted a protein of 596 amino acids with a sequence homologous to that of a superfamily of sugar transporters. Hydropathy analysis suggested that the secondary structure of the PHO84 protein consists of two blocks of six transmembrane domains separated by 74 amino acid residues. The cloned PH084 DNA restored the Pi transport activity of pho84 mutant cells. The PHO84 transcription was regulated by Pi like those of the PHO5, PHO8, and PHO81 genes. A PHO84-lacZ fusion gene produced beta-galactosidase activity under the regulation of Pi, and the activity was suggested to be bound to a membrane fraction. Gene disruption of PHO84 was not lethal. By comparison of nucleotide sequences and by tetrad analysis with GAL80 as a standard, the PHO84 locus was mapped at a site beside the TUB3 locus on the left arm of chromosome XIII.

Yeast coactivator MBF1 mediates GCN4-dependent transcriptional activation.

Transcriptional coactivators play a crucial role in gene expression by communicating between regulatory factors and the basal transcription machinery. The coactivator multiprotein bridging factor 1 (MBF1) was originally identified as a bridging molecule that connects the Drosophila nuclear receptor FTZ-F1 and TATA-binding protein (TBP). The MBF1 sequence is highly conserved across species from Saccharomyces cerevisiae to human. Here we provide evidence acquired in vitro and in vivo that yeast MBF1 mediates GCN4-dependent transcriptional activation by bridging the DNA-binding region of GCN4 and TBP. These findings indicate that the coactivator MBF1 functions by recruiting TBP to promoters where DNA-binding regulators are bound.

Conservation of histone binding and transcriptional repressor functions in a Schizosaccharomyces pombe Tup1p homolog.

The Ssn6p-Tup1p corepressor complex is important to the regulation of several diverse genes in Saccharomyces cerevisiae and serves as a model for corepressor functions. To investigate the evolutionary conservation of these functions, sequences homologous to the S. cerevisiae TUP1 gene were cloned from Kluyveromyces lactis (TUP1) and Schizosaccharomyces pombe (tup11(+)). Interestingly, while the K. lactis TUP1 gene complemented an S. cerevisiae tup1 null mutation, the S. pombe tup11(+) gene did not, even when expressed under the control of the S. cerevisiae TUP1 promoter. However, an S. pombe Tup11p-LexA fusion protein repressed transcription of a corresponding reporter gene, indicating that this Tup1p homolog has intrinsic repressor activity. Moreover, a chimeric protein containing the amino-terminal Ssn6p-binding domain of S. cerevisiae Tup1p and 544 amino acids from the C-terminal region of S. pombe Tup11p complemented the S. cerevisiae tup1 mutation. The failure of native S. pombe Tup11p to complement loss of Tup1p functions in S. cerevisiae corresponds to an inability to bind to S. cerevisiae Ssn6p in vitro. Disruption of tup11(+) in combination with a disruption of tup12(+), another TUP1 homolog gene in S. pombe, causes a defect in glucose repression of fbp1(+), suggesting that S. pombe Tup1p homologs function as repressors in S. pombe. Furthermore, Tup11p binds specifically to histones H3 and H4 in vitro, indicating that both the repression and histone binding functions of Tup1p-related proteins are conserved across species.

GCD2, a translational repressor of the GCN4 gene, has a general function in the initiation of protein synthesis in Saccharomyces cerevisiae.

The GCD2 protein is a translational repressor of GCN4, the transcriptional activator of multiple amino acid biosynthetic genes in Saccharomyces cerevisiae. We present evidence that GCD2 has a general function in the initiation of protein synthesis in addition to its gene-specific role in translational control of GCN4 expression. Two temperature-sensitive lethal gcd2 mutations result in sensitivity to inhibitors of protein synthesis at the permissive temperature, and the gcd2-503 mutation leads to reduced incorporation of labeled leucine into total protein following a shift to the restrictive temperature of 36 degrees C. The gcd2-503 mutation also results in polysome runoff, accumulation of inactive 80S ribosomal couples, and accumulation of at least one of the subunits of the general translation initiation factor 2 (eIF-2 alpha) in 43S-48S particles following a shift to the restrictive temperature. The gcd2-502 mutation causes accumulation of 40S subunits in polysomes, known as halfmers, that are indicative of reduced 40S-60S subunit joining at the initiation codon. These phenotypes suggest that GCD2 functions in the translation initiation pathway at a step following the binding of eIF-2.GTP.Met-tRNA(iMet) to 40S ribosomal subunits. consistent with this hypothesis, we found that inhibiting 40S-60S subunit joining by deleting one copy (RPL16B) of the duplicated gene encoding the 60S ribosomal protein L16 qualitatively mimics the phenotype of gcd2 mutations in causing derepression of GCN4 expression under nonstarvation conditions. However, deletion of RPL16B also prevents efficient derepression of GCN4 under starvation conditions, indicating that lowering the concentration of 60S subunits and reducing GCD2 function affect translation initiation at GCN4 in different ways. This distinction is in accord with a recently proposed model for GCN4 translational control in which ribosomal reinitiation at short upstream open reading frames in the leader of GCN4 mRNA is suppressed under amino acid starvation conditions to allow for increased reinitiation at the GCN4 start codon.

Mating type control in Saccharomyces cerevisiae: a frameshift mutation at the common DNA sequence, X, of the HML alpha locus.

A mutation defective in the homothallic switching of mating type alleles, designated hml alpha-2, has previously been characterized. The mutation occurred in a cell having the HO MATa HML alpha HMRa genotype, and the mutant culture consisted of ca. 10% a mating type cells, 90% nonmater cells of haploid cell size, and 0.1% sporogenous diploid cells. Genetic analyses revealed that nonmater haploid cells have a defect in the alpha 2 cistron at the MAT locus. This defect was probably caused by transposition of a cassette originating from the hml alpha-2 allele by the process of the homothallic mating type switch. That the MAT locus of the nonmater cells is occupied by a DNA fragment indistinguishable from the Y alpha sequence in electrophoretic mobility was demonstrated by Southern hybridization of the EcoRI-HindIII fragment encoding the MAT locus with a cloned HML alpha gene as the probe. The hml alpha-2 mutation was revealed to be a one-base-pair deletion at the ninth base pair in the X region from the X and Y boundary of the HML locus. This mutation gave rise to a shift in the open reading frame of the alpha 2 cistron. A molecular mechanism for the mating type switch associated with the occurrence of sporogenous diploid cells in the mutant culture is discussed.

Mating-type control in Saccharomyces cerevisiae: isolation and characterization of mutants defective in repression by a1-alpha 2.

The alpha 2 protein, the product of the MAT alpha 2 cistron, represses various genes specific to the a mating type (alpha 2 repression), and when combined with the MATa1 gene product, it represses MAT alpha 1 and various haploid-specific genes (a1-alpha 2 repression). One target of a1-alpha 2 repression is RME1, which is a negative regulator of a/alpha-specific genes. We have isolated 13 recessive mutants whose a1-alpha 2 repression is defective but which retain alpha 2 repression in a genetic background of ho MATa HML alpha HMRa sir3 or ho MAT alpha HMRa HMRa sir3. These mutations can be divided into three different classes. One class contains a missense mutation, designated hml alpha 2-102, in the alpha 2 cistron of HML, and another class contains two mat alpha 2-202, in the MAT alpha locus. These three mutants each have an amino acid substitution of tyrosine or acid substitution of tyrosine or phenylalanine for cysteine at the 33rd codon from the translation initiation codon in the alpha 2 cistron of HML alpha or MAT alpha. The remaining 10 mutants make up the third class and form a single complementation group, having mutations designated aar1 (a1-alpha 2 repression), at a gene other than MAT, HML, HMR, RME1, or the four SIR genes. Although a diploid cell homozygous for the aarl and sir3 mutations and for the MATa, HML alpha, and HMRa alleles showed alpha mating type, it could sporulate and gave rise to asci containing four alpha mating-type spores. These facts indicate that the domain for alpha2 repression is separable from that for a1-alpha2 protein interaction or complex formation in the alpha2 protein and that an additional regulation gene, AAR1, is associated with the a1-alpha2 repression of the alpha1 cistron and haploid-specific genes.

Functional equivalence and co-dominance of homothallic genes HM alpha/hm alpha and HMa/hma in Saccharomyces yeasts.

The specificity of mating type in Saccharomyces yeasts is controlled by a pair of alleles, a and alpha, on chromosome III. They are mutually interconverted by the function of three kinds of homothallic genes, each consisting of a single pair of alleles, HO/ho, HM alpha/hma alpha and HMa/hma. For the a to alpha conversion, HO HM alpha, HMa, HO hm alpha HMa and HO hma alpha hma genotypes are effective; whereas the alpha to a conversion occurs in HO HM alpha HMa, HO HM alpha hma and HO hm alpha hma cells. To explain these observations, NAUMOV and TOLSTORUKOV (1973) and HARASHIMA, NOGI and OSHIMA (1974) suggested that hma and HM alpha are functionally equivalent and effective for the alpha to a conversion in combination with HO; whereas, hm alpha and HMa are functionally equivalent and effective for the a to alpha conversion with the function of HO. To test this idea and to compare it with two other possible mechanisms, some of the tetrad segregants from four kinds of a/a/alpha/alpha tetraploids homozygous for the HO allele and for one of the HM alpha/hm alpha and HMa/hma loci, while heterozygous for the other one with +/+/-/- configuration, were investigated with respect to their thallism by self-sporulation. Results indicated the functional equivalence of both the HM alpha and hma alleles and the hm alpha and HMa alleles in mating-type conversion, and the co-dominance of the alleles of each locus. From the findings and other data, we agree with the revision of the nomenclature of the HM alpha/hm alpha and HMa/hma genes to HMRa/HMR alpha and HML alpha/HMLa, respectively.

Mapping of the homothallic genes, HM alpha and HMa, in Saccharomyces yeasts.

Two of the three homothallic genes, HM alpha and HMa, showed direct linkage to the mating-type locus at approximately 73 and 98 strans (57 and 65 centimorgans [cM], respectively, whereas, the other, HO, showed no linkage to 25 standard markers distributed over 17 chromosomes including the mating-type locus. To determine whether the HM alpha and HMa loci located on the left or right side of the mating-type locus, equations for three factor analysis of three linked genes were derived. Tetrad data were collected and were compared with expected values by chi 2 statistics. Calculations indicated that the HM alpha gene is probably located on the right arm at 95 strans (65 cM) from the centromere and the HMa locus at approximately 90 strans (64 cM) on the left arm of chromosome III.