The Roan locus is responsible for the coat coloration of Belgian Blue and Shorthorn cattle. The solid-colored and white animals are homozygotes, and the roan animals, with intermingled colored and white hairs, are heterozygous. The roan phenotype was mapped to cattle Chromosome (Chr) 5 with microsatellites, and a candidate gene was proposed (Charlier et al. Mamm Genome 7, 138, 1996). PCR primers to the exons of this candidate gene, the steel locus or mast cell growth factor (MGF) were designed. Solid-colored and white animals were sequenced. A missense mutation at 654 bp (amino acid 193, Ala --> Asp) was detected in these two groups. A PCR-RFLP was designed to this single base pair change, and 143 animals in total (Belgian Blue, Shorthorn, and various other breeds) were screened. In addition, the Canadian Beef Cattle Reference Herd (http://skyway. usask.ca/ approximately schmutz) was used to verify Mendelian inheritance of this marker with the phenotypic inheritance of roan. Our data suggest that this mutation in the bovine MGF gene is responsible for the roan phenotype.
Schizosaccharomyces pombe utilizes two opposing signaling pathways to sense and respond to its nutritional environment. Glucose detection triggers a cyclic AMP signal to activate protein kinase A (PKA), while glucose or nitrogen starvation activates the Spc1/Sty1 stress-activated protein kinase (SAPK). One process controlled by these pathways is fbp1 ؉ transcription, which is glucose repressed. In this study, we isolated strains carrying mutations that reduce high-level fbp1 ؉ transcription conferred by the loss of adenylate cyclase (git2⌬), including both wis1 ؊ (SAPK kinase) and spc1 ؊ (SAPK) mutants. While characterizing the git2⌬ suppressor strains, we found that the git2⌬ parental strains are KCl sensitive, though not osmotically sensitive. Of 102 git2⌬ suppressor strains, 17 strains display KCl-resistant growth and comprise a single linkage group, carrying mutations in the cgs1 ؉ PKA regulatory subunit gene. Surprisingly, some of these mutants are mostly wild type for mating and stationary-phase viability, unlike the previously characterized cgs1-1 mutant, while showing a significant defect in fbp1-lacZ expression. Thus, certain cgs1 ؊ mutant alleles dramatically affect some PKAregulated processes while having little effect on others. We demonstrate that the PKA and SAPK pathways regulate both cgs1 ؉ and pka1 ؉ transcription, providing a mechanism for cross talk between these two antagonistically acting pathways and feedback regulation of the PKA pathway. Finally, strains defective in both the PKA and SAPK pathways display transcriptional regulation of cgs1 ؉ and pka1 ؉ , suggesting the presence of a third glucose-responsive signaling pathway.Eukaryotic cells employ a variety of signal transduction pathways to regulate growth and developmental responses to changes in their environment. Often, more than one signal transduction pathway regulates a given biological process. Signals generated by one pathway may moderate the function of other signaling pathways, a phenomenon referred to as cross talk. Alternatively, signaling pathways may act independently to produce a regulatory outcome.The fission yeast Schizosaccharomyces pombe regulates many growth and developmental processes in response to nutrient conditions through the action of two opposing signal transduction pathways. Glucose triggers the activation of adenylate cyclase, resulting in a cyclic AMP (cAMP) signal, which activates the cAMP-dependent protein kinase A (PKA) (3,15,24). Nutrient starvation activates a stress-activated protein kinase (SAPK) pathway, which is also activated by osmotic, oxidative, and heat stress (8,10,31,34). Cells lacking adenylate cyclase (git2 ϩ /cyr1 ϩ ) display characteristics of glucose-starved cells even while growing in nutrient-rich conditions in that they efficiently mate and sporulate and they actively transcribe the fbp1 ϩ gene, which is normally subject to glucose repression (15, 23). Cells carrying mutations affecting the Wis1 SAPK kinase (SAPKK) or the Spc1/Sty1 SAPK fail to respond to stress resulting in tempera...
The Schizosaccharomyces pombe fbp1 gene, encoding fructose-1,6-bisphosphatase, is transcriptionally repressed by glucose. Mutations that confer constitutive fbp1 transcription identify git (glucose-insensitive transcription) genes that encode components of a cyclic AMP (cAMP) signaling pathway required for adenylate cyclase activation. Four of these genes encode the three subunits of a heterotrimeric G protein (gpa2, git5, and git11) and a G protein-coupled receptor (git3). Three additional genes, git1, git7, and git10, act in parallel to or downstream from the G protein genes. Here, we describe the cloning and characterization of the git7 gene. The Git7p protein is a member of the Saccharomyces cerevisiae Sgt1p protein family. In budding yeast, Sgt1p associates with Skp1p and plays an essential role in kinetochore assembly, while in Arabidopsis, a pair of SGT1 proteins have been found to be involved in plant disease resistance through an interaction with RAR1. Like S. cerevisiae Sgt1p, Git7p is essential, but this requirement appears to be due to roles in septation and cell wall integrity, which are unrelated to cAMP signaling, as S. pombe cells lacking either adenylate cyclase or protein kinase A are viable. In addition, git7 mutants are sensitive to the microtubule-destabilizing drug benomyl, although they do not display a chromosome stability defect. Two alleles of git7 that are functional for cell growth and septation but defective for glucose-triggered cAMP signaling encode proteins that are altered in the highly conserved carboxy terminus. The S. cerevisiae and human SGT1 genes both suppress git7-93 but not git7-235 for glucose repression of fbp1 transcription and benomyl sensitivity. This allele-specific suppression indicates that the Git7p/Sgt1p proteins may act as multimers, such that Git7-93p but not Git7-235p can deliver the orthologous proteins to species-specific targets. Our studies suggest that members of the Git7p/Sgt1p protein family may play a conserved role in the regulation of adenylate cyclase activation in S. pombe, S. cerevisiae, and humans.
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