Cis- and trans-acting functions required for endocytosis of the yeast pheromone receptors.

The Saccharomyces cerevisiae a-factor receptor (STE3) is subject to two modes of endocytosis: a constitutive process that occurs in the absence of ligand and a regulated process that is triggered by binding of ligand. Both processes result in delivery of the receptor to the vacuole for degradation. Receptor mutants deleted for part of the COOH-terminal cytoplasmic domain are disabled for constitutive, but not ligand-dependent internalization. Trans-acting mutants that impair constitutive endocytosis have been isolated. One of these, ren1-1, is blocked at a late step in the endocytic pathway, as receptor accumulates in a prevacuolar endosome-like compartment. REN1 is identical to VPS2, a gene required for delivery of newly synthesized vacuolar enzymes to the vacuole. Based on this identity, we suggest a model in which the transport pathways to the vacuole--the endocytic pathway and the vacuolar biogenesis pathway--merge at an intermediate endocytic compartment. As receptor also accumulates at the surface of ren1 cells, receptor may recycle from the putative endosome to the surface, or REN1 may also be required to carry out an early step in endocytosis.

A complex of nuclear pore proteins required for pore function.

A family of proteins bearing novel N-acetylglucosamine residues has previously been found to be required to form functional nuclear pores. To begin to determine which of the proteins in this family are essential for pore function, antisera were raised to each of three members of the family, p62, p58, and p54. With these antisera, it was possible to deplete nuclear reconstitution extracts of the proteins and to test the depleted nuclei for nuclear transport. In the course of the experiments, it was found that the three proteins exist as a complex; antisera to any one, while specific on a protein blot, coimmunoprecipitated all three proteins. This complex of pore proteins is stable to 2 M salt, 2 M urea, and the detergent Mega 10, indicating the presence of specific and tight protein-protein interactions. By gel filtration, the complex has a molecular mass of 550-600 kD. Nuclei containing pores depleted of the complex are found to be defective for nuclear transport; moreover, we observe a strict linear correlation between the amount of complex present in nuclei and the amount of nuclear transport of which those nuclei are capable. Thus, the p62-p58-p54 complex defines a group of proteins with strong protein-protein interactions that form a unit of pore structure essential for pore function.

Identification and characterization of FAR3, a gene required for pheromone-mediated G1 arrest in Saccharomyces cerevisiae.

In haploid Saccharomyces cerevisiae cells, mating pheromones activate a signal transduction pathway that leads to cell cycle arrest in the G1 phase and to transcription induction of genes that promote conjugation. To identify genes that link the signal transduction pathway and the cell cycle machinery, we developed a selection strategy to isolate yeast mutants specifically defective for G1 arrest. Several of these mutants identified previously known genes, including CLN3, FUS3, and FAR1. In addition, a new gene, FAR3, was identified and characterized. FAR3 encodes a novel protein of 204 amino acid residues that is dispensable for viability. Northern blot experiments indicated that FAR3 expression is constitutive with respect to cell type, pheromone treatment, and cell cycle position. As a first step toward elucidating the mechanism by which Far3 promotes pheromone-mediated G1 arrest, we performed genetic and molecular experiments to test the possibility that Far3 participates in one of the heretofore characterized mechanisms, namely Fus3/Far1-mediated inhibition of Cdc28-Cln kinase activity, G1 cyclin gene repression, and G1 cyclin protein turnover. Our data indicate that Far3 effects G1 arrest by a mechanism distinct from those previously known.

Defects in protein glycosylation cause SHO1-dependent activation of a STE12 signaling pathway in yeast.

In haploid Saccharomyces cerevisiae, mating occurs by activation of the pheromone response pathway. A genetic selection for mutants that activate this pathway uncovered a class of mutants defective in cell wall integrity. Partial loss-of-function alleles of PGI1, PMI40, PSA1, DPM1, ALG1, MNN10, SPT14, and OCH1, genes required for mannose utilization and protein glycosylation, activated a pheromone-response-pathway-dependent reporter (FUS1) in cells lacking a basal signal (ste4). Pathway activation was suppressed by the addition of mannose to hexose isomerase mutants pgi1-101 and pmi40-101, which bypassed the requirement for mannose biosynthesis in these mutants. Pathway activation was also suppressed in dpm1-101 mutants by plasmids that contained RER2 or PSA1, which produce the substrates for Dpm1. Activation of FUS1 transcription in the mannose utilization/protein glycosylation mutants required some but not all proteins from three different signaling pathways: the pheromone response, invasive growth, and HOG pathways. We specifically suggest that a Sho1 --> Ste20/Ste50 --> Ste11 --> Ste7 --> Kss1 --> Ste12 pathway is responsible for activation of FUS1 transcription in these mutants. Because loss of pheromone response pathway components leads to a synthetic growth defect in mannose utilization/protein glycosylation mutants, we suggest that the Sho1 --> Ste12 pathway contributes to maintenance of cell wall integrity in vegetative cells.

Human CPR (cell cycle progression restoration) genes impart a Far- phenotype on yeast cells.

Regulated cell cycle progression depends on the proper integration of growth control pathways with the basic cell cycle machinery. While many of the central molecules such as cyclins, CDKs, and CKIs are known, and many of the kinases and phosphatases that modify the CDKs have been identified, little is known about the additional layers of regulation that impinge upon these molecules. To identify new regulators of cell proliferation, we have selected for human and yeast cDNAs that when overexpressed were capable of specifically overcoming G1 arrest signals from the cell cycle branch of the mating pheromone pathway, while still maintaining the integrity of the transcriptional induction branch. We have identified 13 human CPR (cell cycle progression restoration) genes and 11 yeast OPY (overproduction-induced pheromone-resistant yeast) genes that specifically block the G1 arrest by mating pheromone. The CPR genes represent a variety of biochemical functions including a new cyclin, a tumor suppressor binding protein, chaperones, transcription factors, translation factors, RNA-binding proteins, as well as novel proteins. Several CPR genes require individual CLNs to promote pheromone resistance and those that require CLN3 increase the basal levels of Cln3 protein. Moreover, several of the yeast OPY genes have overlapping functions with the human CPR genes, indicating a possible conservation of roles.

Cloning and characterization of the Saccharomyces cerevisiae LYS7 gene: evidence for function outside of lysine biosynthesis.

The Saccharomyces cerevisiae LYS7 gene has been cloned based on its genetic map position and complementation of a lys7 mutant. The 1453-bp sequence contains an open reading frame (ORF) that predicts a unique 249 amino acid (aa) protein. A Northern blot experiment demonstrated that LYS7 transcription was not regulated by lysine-specific or general aa control mechanisms. To investigate the effects of total loss of LYS7 function, we created a complete deletion of the gene and introduced this allele into wild-type yeast. The lys7 delta mutant requires lysine and simultaneously displays an array of phenotypes that include pH and temperature sensitivity. The pleiotropic phenotypes of the lys7 delta mutant and the constitutive transcription pattern are at odds with the hypothesis that Lys7p functions solely in the lysine biosynthesis pathway.

[Experiences in the determination of hepatitis B antigen in acute viral hepatitis]. / Zkusenosti s vysetrováním antigenu hepatitidy B u akutní virusové hepatitidy

The antigen of hepatitis B was repeatedly examined in 1356 adults patients with acute viral hepatitis. In 701 patients the HBAg was positive at the beginning of illness and in 657 was negative. The maximum of the negative HBAg results could be found in the lower age groups, whereas the maximum of the positive HBAg results was shifted to the 5th and 6th decade. In HBAg positive cases of hepatitis more numerous anicteric and asymptomatic forms could be observed on the other hand, however, at the same time also o more cholestatic forms and subacute necrotizing and malignant forms appeared. The HBAg positive hepatitis had on average also a more serious form and course. From the epidemiological point of view the admission to the hospital, which preceded in 51% of patients appeared as the most important factor. In 16.3% of patients the HBAg postivity persisted still 6 months after the discharge from the hospital.

[Clinical problems in non-A, non-B viral hepatitis. III. The course of non-A, non-B viral hepatitis in the chronic stages]. / Klinická problematika virových hepatitid non-A, non-B. III. Prubeh chronického stadia virové hepatitidy non-A, non-B.

Investigation of a group of 231 patients with viral hepatitis non-A, non-B (HNANB) revealed that the majority of cases is of the parenteral type (60.17%) and the remainder was without parenteral procedures. The course of HNANB was icteric in the majority (72.55%). On check-up examination one year after the onset of the acute stage the pathological clinical and laboratory finding, i.e. chronic liver disease still persisted in 31.6%. A follow-up of the patients in the course of six years revealed that the ratio of serious sequelae (chronic active hepatitis and cirrhosis of the liver) is significant and increases with time and thus already after two years these serious diagnoses predominate over the number of patients with chronic persistent hepatitis. The chi2 test revealed that there is no sexual difference as regards the development of the chronic stage of HNANB, that the chronic stage develops in both basic types of HNANB (in the parenteral and the epidemic type) but it is significantly more frequent in the parenteral type. The development of the chronic stage is equally frequent after icteric and anicteric forms. In patients who recovered completely within one year (68.39%) the convalescence was protracted and normalization of the clinical and biochemical finding occurred later than in patients with viral hepatitis A and B, hospitalized during the same period.

Localization of the FAR3 gene: genetic mapping and molecular cloning using a chromosome walk-'n'-roll strategy.

FAR3 is a newly-discovered yeast gene required specifically for pheromone-mediated cell cycle arrest. I have used strains harboring the far3-1 mutation to map the gene to the right arm of chromosome XIII, establishing the gene order CEN13-LYS7-MCM1-FAR3. I cloned the FAR3 gene based on its genetic map position using a strategy that combined chromosome walking and a related technique termed 'chromosome rolling'. In addition to the genetic and physical localization of FAR3, I present data that suggest corrections to the tentative map positions of VAN1 and ARG80.

Identifying tagged transposon insertion sites in yeast by direct genomic sequencing.

Tagged transposons are powerful tools for large-scale studies of gene expression, protein localization, and gene disruption in Saccharomyces cerevisiae. The current techniques used to identify transposon insertion sites in the yeast genome require a DNA amplification step that can be time-consuming and problematic. We show that the DNA amplification step can be bypassed. Insertion sites can be identified rapidly and reliably by direct genomic sequencing using a transposon-specific primer, BigDye-labelled terminators, and an automated sequencer. Direct genomic sequencing can also save time on the genetic analysis phase of transposon-based projects.

The trp1- delta FA designer deletion for PCR-based gene functional analysis in Saccharomyces cerevisiae.

PCR-based gene deletion and modification are now common techniques for rapid gene manipulation in the yeast Saccharomyces cerevisiae. The techniques work best when the host strain lacks sequence homology to the PCR-amplified selectable markers. One of the most versatile sets of PCR deletion/modification vectors is the pFA system described by Longtine et al.(1998), which is based on both heterologous (kanMX6 and HIS3MX6) and homologous (TRP1) markers. Here we describe the trp1-DeltaFA designer deletion allele that removes precisely from the genome TRP1 sequences carried in the pFA vectors. The trp1-DeltaFA allele can be introduced easily into TRP1 and most trp1 starting strains, and its use increases the frequency of correct integrants when using the pFA system's TRP1-based constructs. Unlike trp1-Delta1, trp1-DeltaFA does not remove neighbouring GAL3 upstream activating sequences and therefore does not interfere with GAL gene induction.