Genetic interaction of DED1 encoding a putative ATP-dependent RNA helicase with SRM1 encoding a mammalian RCC1 homolog in Saccharomyces cerevisiae

 The Saccharomyces cerevisiae temperature-sensitive mutants srm1-1, mtr1-2 and prp20-1 carry alleles of a gene encoding a homolog of mammalian RCC1. In order to identify a protein interacting with RCC1, a series of suppressors of the srm1-1 mutation were isolated as cold-sensitive mutants and one of the mutants, designated ded1-21, was found to be defective in the DED1 gene. The double mutant, srm1-1 ded1-21, could grow at 35° C, but not at 37° C. A revertant of srm1-1 ded1-21 that became able to grow at 37° C acquired another mutation in the SRM1 gene, indicating the tight relationship between SRM1 and DED1. In all the rcc1 ^- strains examined, the amount of mutated SRM1 proteins was reduced or not detectable at the nonpermissive temperature. While mutated SRM1 protein was stabilized in all of the rcc1 ^- strains by the ded1-21 mutation, the ded1-21 mutation suppressed both srm1-1 and mtr1-2, but not the prp20-1 mutation, contrary to the previous finding that overproduction of the S. cerevisiae Ran homolog GSP1 suppresses prp20-1, but not srm1-1 or mtr1-2. Received: 20 March 1996/Accepted: 1 July 1996     

Evolutionary study of multigenic families mapping close to the human MHC class I region

Summary During a search for novel coding sequences within the human MHC class I region (chromosome 6p21.3), we found an exon (named B30-2) coding for a 166-amino-acid peptide which is very similar to the C-terminal domain of several coding sequences: human 52-kD Sjögren's syndrome nuclear antigen A/Ro (SS-A/Ro) and ret finger protein (RFP), Xenopus nuclear factor 7 (XNF7), and bovine butyrophilin. The first three of these proteins share similarities over the whole length of the molecule whereas butyrophilin is similar in the C-terminal domain. The N-terminal domain of butyrophilin is similar to rat myelin/oligodendrocyte glycoprotein (MOG) and chicken B blood group system (B-G) protein. These domains are components of a new subfamily of the immunoglobulin superfamily (IgSF). Butyrophilin is thus a mosaic protein composed of the MOG/B-G Ig-like domain and the C-terminal domain of 52-kD SS-A/Ro, RFP, and XNF7 (1330-2-like domain). Moreover, in situ hybridization shows that RFP, butyrophilin, and MOG map to the human chromosome 6p2l.3-6p22 region and are thus close to the MHC class I genes. It is therefore possible that the butyrophilin gene is the product of an exon shuffling event which occurred between ancestors of the RFP and MOG genes. To our knowledge, this is the first example of the colocalization of a chimeric gene and its putative progenitors. Finally, regulatory protein T-lymphocyte 1 (Rpt-1) shares similarities with the N-terminal halves of RFP, 52-kD SS-A/Ro, and XNF7, but not with the B30-2-like domain. We show that the ancestral Rpt-l gene evolved by overprinting. Correspondence to: P. Pontarotti     

A model for neural representation of binocular disparity in striate cortex: distributed representation and veto mechanism

A model in striate cortex is proposed for a distributed neural representation of binocular disparity with a simple cell. In the model, disparity is represented by far, near and tuned inhibitory simple cells. However, the representation will be vetoed by model cells where disparity is excessively large. The veto mechanism consists of a neural network of the model cell which received output from simple cells and which interacts with neighbors. The mechanism is necessary, the model cell responds like a simple cell, and the network is physiologically plausible in the brain. Computer simulation on the neural network model with random dot stereography indicates reasonable performance.     

Insuppressibility of plasma glucagon by orally or intravenously administered glucose in diabetes mellitus

In order to study the response of pancreatic alpha cells to the change blood glucose, plasma pancreatic glucagon levels were measured after glucose loading given orally (50g) or intravenously (25g) in twenty-two normal controls and eighty untreated diabetics. Basal plasma pancreatic glucagon levels did not differ significantly in the two groups. However, oral or intravenous glucose administration caused a decrease in plasma pancreatic glucagon in normal subjects but not in diabetics. In "moderate" or "severe" diabetics, plasma pancreatic glucagon tended to increase paradoxically following oral glucose loading. To evaluate the sensitivity of pancreatic alpha cells to glucose, we calculated the index, -sigma delta IRG/sigma delta BS, after oral glucose loading. It was 1.96 +/- 0.57 in normal subjects, and significantly higher than in "mild" (0.11 +/- 0.05), "moderate" (-0.002 +/- 0.06) and "severe" (-0.09 +/- 0.07) diabetics. These results demonstrate the insensitivity of alpha cells to hyperglycemia in patients with diabetes mellitus as compared with normal subjects.     

Mechanism of Photoregulated Carotenogenesis in Rhodotorula minuta IV. Effect of Light on the Production of Ergosterol and Phytoene and on the Composition of Carotenoid Pigments

The effect of light on the production of ergosterol and phytoeneand on the composition of carotenoids in Rhodotorula minutawas studied to determine which part of the pathway of carotenoidsynthesis regulated by light. The ergosterol content in the cells was in the range of 3.4–3.6mg/g dry cells regardless of the presence or absence of illuminationand the light intensity. The phytoene production in the cellswas markedly stimulated by light and was dependent on the lightintensity according to the amount of carotenoid pigments produced.In addition, the ratio of phytoene to carotenoid was in therange of 0.36–0.44, regardless of the presence or absenceof illumination and the light intensity. The fact that the ratio of carotenoid fractionated on the basisof the functional group involved in each carotenoid to the totalamount of carotenoid was almost constant regardless of the lightintensity suggested that the composition of the carotenoidssynthesized in the cells is not affected by light. It was deduced from these results that light induced the productionof enzyme(s) required for phytoene biosynthesis in Rhodotorulaminuta. (Received November 7, 1981; Accepted March 19, 1982)     

Role of the duodenum in motilin release

In order to study the regulatory mechanism of motilin release, plasma motilin was measured in healthy dogs during the fasting state and after the ingestion of ordinary nutrient. Fasting plasma motilin levels were found to fluctuate intermittently, but ingestion of a meal completely abolished the intermittent motilin release and resulted in low motilin levels lasting for 6–8 h. To clarify the role of the duodenum in this motilin release, an operation was performed in five dogs by which we excluded from the alimentary tract the upper half of the small intestine not including the duodenum from a point 2 cm below the larger pancreatic duct. After this operation meal ingestion still caused a decrease in plasma motilin levels. However, after a modified version of the operation was performed in 5 other dogs by which the upper half of the small intestine together with the duodenum was transected at the pyloric ring, plasma motilin was not suppressed by meal ingestion. These results suggest that motilin secretion is regulated by nutrient ingestion and that the passage of nutrients through the duodenum plays a important role in its regulation.