Schizosaccharomyces pombe gad7+ encodes a phosphoprotein with a bZIP domain, which is required for proper G1 arrest and gene expression under nitrogen starvation.

BACKGROUND: Fission yeast cells arrest at G1 phase when starved of nitrogen. The molecular mechanism that ensures this arrest is poorly understood. We took a genetic approach to this problem. RESULTS: The fission yeast gad7-1 mutant failed to arrest at G1 when starved of nitrogen, and was poor in mating and sporulation. The gad7 gene was cloned by complementation. The deduced gad7 gene product was a bZIP protein of 566 amino acids, which could bind to the CRE (cAMP response element) sequence in vitro. Disruption of gad7 resulted in the same phenotypes as gad7-1. Expression of ste11, which encodes a key transcription factor for sexual development, was not inducible in the disruptant. Gad7 was co-immunoprecipitated with another bZIP protein Pcr1, suggesting that the two proteins form a heterodimer in vivo. Gad7 was phosphorylated, and the state of its phosphorylation appeared to be modified in pka1delta or wis1delta cells. CONCLUSIONS: Gad7, a CRE-binding protein that cooperates with Pcr1, is required for proper G1 arrest and gene expression under nitrogen starvation. Gad7 is a phosphoprotein, whose activity may be regulated by protein kinases including the cAMP-dependent protein kinase (Pka1) and Wis1 osmosensory MAP kinase kinase.

Schizosaccharomyces pombe zfs1+ encoding a zinc-finger protein functions in the mating pheromone recognition pathway.

We isolated the Schizosaccharomyces pombe zfs1 gene as a multicopy suppressor of the sterility caused by overexpression of a double-stranded RNase. The deduced zfs1 gene product of 404 amino acids showed similarity to a mouse growth factor-inducible nuclear protein Nup475. Its C-terminal region carried two putative zinc-fingers, both of which should be intact for the protein to be functional as the suppressor. This protein appeared to localize in nuclei. Disruption of zfs1 was not lethal but conferred deficiency in mating and sporulation. Activation of transcription in response to the mating pheromone signaling was greatly reduced in the zfs1-disrupted cells. The mating deficiency of the zfs1-disruptant was suppressed partially by overexpression of either gpa1, ras1, byr1, or byr2, which are involved in the transmission of the pheromone signal. Disruption of zfs1 reduced both hypersensitivity of the ras1Val17 mutant to the mating pheromone and uncontrolled mating response caused by mutational activation of Gpa1, the G protein alpha subunit coupled to the mating pheromone receptors. However, overexpression of zfs1 could not bypass complete loss of function of either gpa1, ras1, byr1, or byr2. These observations indicate that the function of zfs1 is involved in the mating pheromone signaling pathway, and are consistent with its function being required to fully activate a factor in this pathway, either directly or indirectly.

New technique using intraductal ultrasonography for the diagnosis of diseases of the pancreatobiliary system.

Intraductal ultrasonography (IDUS), a new technique for visualizing arterial structures, operates at an ultrasound frequency of 30 MHz to produce high resolution, cross-sectional images in real time. The purpose of this study was to provide a basis for interpreting IDUS images in vitro. We also attempted to determine the clinical usefulness of the IDUS system in diagnosing pancreatobiliary diseases in vivo. IDUS echograms of both the bile duct (BD) and main pancreatic duct (MPD) from autopsy specimens of 15 patients demonstrated three distinct layers with a fine reticular pattern in the pancreas in vitro. In clinical cases, the MPD and BD of four patients could be scanned by inserting the IDUS catheter via the major papilla without requiring endoscopic sphincterotomy. We hope that IDUS will become routine in scanning the BD and MPD to achieve early and accurate diagnoses of pancreatobiliary diseases.

Monitoring the pressure of the sphincter of Oddi by percutaneous transhepatic choledochoscopy: new method for evaluating motor function.

The pressure of the sphincter of Oddi was measured in 40 patients using a thin microtransducer introduced via percutaneous transhepatic choledochoscopy. Choledochograms of the Vaterian bile duct were classified into four types: N (normal), I, II and III. Judging from the length of the Vaterian bile duct and the degree of fibrosis observed in the biopsy specimens, duodenal papillitis was found to be more severe in Type III than in Type II. Nevertheless the systolic pressure was significantly lower in Type III. We considered that when duodenal papillitis is considerably advanced, the force of contraction of the sphincter is reduced. In addition, based on choledochoscopic observations, as duodenal papillitis increased in severity, the incidence of an irregular shape at the end of the common bile duct during diastole increased. The indications for endoscopic sphincterotomy were determined based on the pressure of the sphincter of Oddi in patients with normal duodenal papilla. In the 26 patients in whom the procedure was not indicated, no gallstones developed. In the 3 patients in whom the procedure was indicated and performed, gallstones have not developed. However, 3 of the 6 patients in whom the procedure was indicated but not performed developed gallstones. This method is useful in evaluating the motor function of the sphincter of Oddi under relatively physiological conditions.