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1.
Two integral membrane proteins located in the cis-middle and trans-part of the Golgi system acquire sialylated N-linked carbohydrates and display different turnovers and sensitivity to cAMP-dependent phosphorylation 总被引:24,自引:13,他引:11
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The localization and chemical characteristics of two Golgi integral membrane proteins (GIMPs) have been studied using monoclonal antibodies. The two proteins are segregated in different parts of the Golgi system and whereas GIMPc(130 kD) is located in the cis and medial cisternae, GIMPt (100 kD) is confined in the trans-most cisterna and trans-tubular network. Both GIMPs are glycoproteins that contain N- and O-linked carbohydrates. The N-linked carbohydrates were exclusively of the complex type. Although excluded from the trans-side of the Golgi system, where sialylation is believed to occur, GIMPc acquires sialic acid in both its N- and O-linked carbohydrates. Sialic acid was also detected in the N-linked carbohydrates of GIMPt. GIMPc is apparently phosphorylated in the luminal domain in vivo. Phosphorylation occurred exclusively on serine and was stimulated by dibutyryl cyclic AMP. GIMPc and GIMPt displayed half-lives of 20 and 9 h, respectively. 相似文献
2.
Interferon effects upon fluorouracil metabolism by HL-60 cells 总被引:4,自引:0,他引:4
In order to better understand the synergistic antiproliferative effects of interferon in combination with fluorouracil (FUra), we studied effects of alpha 2-interferon upon FUra induced inhibition of thymidylate synthase of HL-60 cells. The 50% inhibitory dose for FUra decreased from approximately 75 microM to 10 microM following interferon treatment, as measured by whole cell activity assays. Enhanced FUra inhibition of cytosolic [3H] - FdUMP binding of interferon treated cells was also noted. FdUMP accumulation following FUra treatment increased over 10 fold in interferon treated cells, but dUMP did not increase. These results suggest that interferon can sensitize cells to FUra inhibition of thymidylate synthase by enhancing accumulation of FdUMP. 相似文献
3.
J G Barriocanal J S Bonifacino L Yuan I V Sandoval 《The Journal of biological chemistry》1986,261(35):16755-16763
The biosynthesis, glycosylation, movement through the Golgi system, transport to lysosomes, and turnover of three lysosomal integral membrane proteins (LIMPSs) have been studied in normal rat kidney cells using specific anti-LIMP monoclonal antibodies. Immunoelectron microscopy studies revealed the presence of LIMPs in secondary lysosomes, Golgi cisterna, and coated and uncoated vesicles located in the trans-Golgi cisterna, area. Pulse-chase experiments recorded LIMP precursors of 27 (LIMP I), 72 (LIMP II), and 86 kDa (LIMP III) and mature LIMPs of 35-50 (LIMP I), 74 (LIMP II), and 90-100 kDa (LIMP III). Time course studies on the acquisition of endoglycosidase H resistance by LIMPs indicated that all three LIMPs moved from the site of their synthesis in the endoplasmic reticulum to the medial Golgi within 30-60 min after their synthesis. All three LIMPs were fully glycosylated before leaving the Golgi system, the process during which LIMP I was retained in the trans side of the organelle. LIMP I reached the lysosomes with a halftime of 2 h and LIMPs II and III with half-times of 1 h after their synthesis by a mechanism that was independent of N-linked carbohydrates. LIMPs free of N-linked carbohydrates displayed much shorter half-lives than fully glycosylated LIMPs, suggesting an important role of the sugars in protecting LIMPs against proteolytic degradation. Double immunofluorescence microscopy experiments showed that LIMP I, LIMP II, and LIMP III are localized in the same lysosomes. 相似文献
4.
Screening of plasmids in non-pathogenic corynebacteria 总被引:1,自引:0,他引:1
H. Sandoval G. del Real L.M. Mateos A. Aguilar J.F. Martín 《FEMS microbiology letters》1985,27(1):93-98
Abstract A screening of plasmids in 25 nonpathogenic coryneform bacteria was carried out. 11 Strains showed at least one plasmid, ranging in size from 4.2 to 55 kb. These plasmids did not encode bacteriocin production or resistance to a number of antibiotics or to ions such as arsenite, mercury(II) and cobalt(II). A detailed study of plasmid pBL100 from Brevibacterium linens is presented. pBL100 has a size of 7.75 kb, and contains single sites for the endonucleases: Hin dIII; Pst I, Bgl II, Eco RI and Bam HI. B. linens is easily and efficiently transformed with vectors derived from pBL1 isolated from Brevibacterium lactofermentum . 相似文献
5.
Nielsen J; Peixoto AA; Piccin A; Costa R; Kyriacou CP; Chalmers D 《Molecular biology and evolution》1994,11(6):839-853
The region of the clock gene period (per) that encodes a repetitive tract
of threonine-glycine (Thr-Gly) pairs has been compared between Dipteran
species both within and outside the Drosophilidae. All the non-
Drosophilidae sequences in this region are short and present a remarkably
stable picture compared to the Drosophilidae, in which the region is much
larger and extremely variable, both in size and composition. The
accelerated evolution in the repetitive region of the Drosophilidae appears
to be mainly due to an expansion of two ancestral repeats, one encoding a
Thr-Gly dipeptide and the other a pentapeptide rich in serine, glycine, and
asparagine or threonine. In some drosophilids the expansion involves a
duplication of the pentapeptide sequence, but in Drosophila pseudoobscura
both the dipeptide and the pentapeptide repeats are present in larger
numbers. In the nondrosophilids, however, the pentapeptide sequence is
represented by one copy and the dipeptide by two copies. These observations
fulfill some of the predictions of recent theoretical models that have
simulated the evolution of repetitive sequences.
相似文献
6.
Yeast aminopeptidase I is post-translationally sorted from the cytosol to the vacuole by a mechanism mediated by its bipartite N-terminal extension. 总被引:2,自引:0,他引:2
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Transport of aminopeptidase I (API) to the vacuole appears to be insensitive to blockage of the secretory pathway. Here we show that the N-terminal extension of the 61 kDa precursor of API (pAPI) is proteolytically processed in two sequential steps. The first step involves proteinase A (PrA) and produces a 55 kDa unstable intermediate (iAPI). The second step involves proteinase B (PrB) and converts iAPI into the 50 kDa stable, mature enzyme (mAPI). Reversion of the cup1 growth phenotype by a pAPI-CUP1 chimera indicates that pAPI is transported to the vacuole by a post-translational mechanism. Deletion of the first 16 amino acids results in accumulation of the truncated protein in the cytosol, indicating that pAPI is actively transported to the vacuole. The chimera pAPI-myc, constructed by fusing a myc tag to the C-terminus of pAPI, was exploited to dissect the mechanism of pAPI transport. Cell fractionation studies show the presence of iAPI-myc and mAPI in a fraction of vacuoles purified by density centrifugation. This and the sequential conversion of pAPI-myc into iAPI-myc and mAPI lacking the myc tag is consistent with insertion of pAPI into the vacuolar membrane through its N-terminal extension. The specific mechanism of API sorting demonstrates a new pathway of protein transport in vacuolar biogenesis. 相似文献
7.
Evolutionary origin of human and primate malarias: evidence from the circumsporozoite protein gene 总被引:8,自引:1,他引:7
We have analyzed the conserved regions of the gene coding for the
circumsporozoite protein (CSP) in 12 species of Plasmodium, the malaria
parasite. The closest evolutionary relative of P. falciparum, the agent of
malignant human malaria, is P. reichenowi, a chimpanzee parasite. This is
consistent with the hypothesis that P. falciparum is an ancient human
parasite, associated with humans since the divergence of the hominids from
their closest hominoid relatives. Three other human Plasmodium species are
each genetically indistinguishable from species parasitic to nonhuman
primates; that is, for the DNA sequences included in our analysis, the
differences between species are not greater than the differences between
strains of the human species. The human P. malariae is indistinguishable
from P. brasilianum, and P. vivax is indistinguishable from P. simium; P.
brasilianum and P. simium are parasitic to New World monkeys. The human P.
vivax-like is indistinguishable from P. simiovale, a parasite of Old World
macaques. We conjecture that P. malariae, P. vivax, and P. vivax-like are
evolutionarily recent human parasites, the first two at least acquired only
within the last several thousand years, and perhaps within the last few
hundred years, after the expansion of human populations in South America
following the European colonizations. We estimate the rate of evolution of
the conserved regions of the CSP gene as 2.46 x 10(-9) per site per year.
The divergence between the P. falciparum and P. reichenowi lineages is
accordingly dated 8.9 Myr ago. The divergence between the three lineages
leading to the human parasites is very ancient, about 100 Myr old between
P. malariae and P. vivax (and P. vivax-like) and about 165 Myr old between
P. falciparum and the other two.
相似文献
8.
Photosynthetic enhancement studies performed at 619 nm (excitation of Systems I and II) and at 446 nm (mainly excitation of System I) revealed an 18% photosynthetic enhancement simultaneously with a 31% reduction in glycolate excretion. This observation supports the hypothesis that some glycolate may be consumed in an oxidation process associated with System I when System II is poorly excited and the supply of electrons from the water splitting process of photosynthesis is low. 相似文献
9.
Marvin H. Bernstein Inez Sandoval Michael B. Curtis Dennis M. Hudson 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1979,129(2):115-118
Summary During heat stress in domestic pigeons (Columba livia, mean mass 0.43 kg) brain temperature (T
B) varied in parallel with colonic temperature (T
c). The difference between these (T
C–T
B=T) averaged 0.7°C and was not significantly altered when the animal breathed through a trachael cannula bypassing the buccopharyngeal cavity. When we sealed the nares and beak in bypass animals, T was significantly reduced but was nevertheless maintained at 0.4°C. When the eyes were sealed as well, however, T was reversed, amounting to –0.4°C. Conversely, with eyes sealed but beak and nares open, T was indistinguishable from that in controls. These results suggest a role for the cornea in evaporative cooling, at least when respiratory evaporation is impaired, and are consistent with the hypothesis that buccopharyngeal and corneal evaporation are coupled to brain cooling. The probable mechanism for this coupling is the flow of venous blood from evaporative surfaces through theretia mirabilia in the temporal areas. Here heat is transferred from the warmer arterial blood flowing through theretia toward the brain to the centrally flowing, cooler venous blood. 相似文献
10.