Deficiency in spliceosome-associated factor CTNNBL1 does not affect ongoing cell cycling but delays exit from quiescence and results in embryonic lethality in mice

CTNNBL1 is an armadillo-repeat protein that associates with the CDC5L/Prp19 complex of the spliceosome. Unlike the majority of spliceosomal proteins (and despite having no obvious homologs), CTNNBL1 is inessential for cell viability as revealed by studies in both vertebrate B cell lines and in fission yeast. Here, however, we show that ablation of CTNNBL1 in the mouse germline results in mid-gestation embryonic lethality but that lineage-specific CTNNBL1 ablation in early B cell precursors does not affect the production and abundance of mature B lymphocytes. However, CTNNBL1-deficient resting B lymphocytes show sluggish exit from quiescence on cell activation, although once entry into cycle has initiated, proliferation and differentiation in response to mitogenic stimuli continue largely unaffected. A similar sluggish exit from quiescence is also observed on reprovision of nutrients to nitrogen-starved CTNNBL1-deficient yeast. The results indicate that, whereas other RNA splicing-associated factors have been connected to cell cycle progression, CTNNBL1 plays no essential role in cycling cells but does fulfill an evolutionarily conserved function in helping cells to undergo efficient exit from quiescence following activation.     

The Interaction between AID and CIB1 Is Nonessential for Antibody Gene Diversification by Gene Conversion or Class Switch Recombination

Activation-induced deaminase (AID) initiates somatic hypermutation, gene conversion and class switch recombination by deaminating variable and switch region DNA cytidines to uridines. AID is predominantly cytoplasmic and must enter the nuclear compartment to initiate these distinct antibody gene diversification reactions. Nuclear AID is relatively short-lived, as it is efficiently exported by a CRM1-dependent mechanism and it is susceptible to proteasome-dependent degradation. To help shed light on mechanisms of post-translational regulation, a yeast-based screen was performed to identify AID-interacting proteins. The calcium and integrin binding protein CIB1 was identified by sequencing and the interaction was confirmed by immunoprecipitation experiments. The AID/CIB1 resisted DNase and RNase treatment, and it is therefore unlikely to be mediated by nucleic acid. The requirement for CIB1 in AID-mediated antibody gene diversification reactions was assessed in CIB1-deficient DT40 cells and in knockout mice, but immunoglobulin gene conversion and class switch recombination appeared normal. The DT40 system was also used to show that CIB1 over-expression has no effect on gene conversion and that AID-EGFP subcellular localization is normal. These combined data demonstrate that CIB1 is not required for AID to mediate antibody gene diversification processes. It remains possible that CIB1 has an alternative, a redundant or a subtle non-limiting regulatory role in AID biology.     

轮状病毒非结构蛋白NSP1与宿主的相互作用

轮状病毒（rotavirus,RV）非结构蛋白1（nonstructural protein 1,NSP1）是轮状病毒逃避宿主天然免疫应答的关键蛋白质。它可以与干扰素调控因子家族（interferon regulatoryfactor family,IRFF）的共同区域结合,阻断干扰素表达的信号通路,降低宿主细胞I型干扰素（type I interferon,IFN-I）的表达,从而抑制宿主天然抗病毒免疫机制的建立。因此,NSP1被认为是轮状病毒的一种重要毒力因子。本文综述了近年来轮状病毒NSP1与宿主相互作用的研究进展。     

Interaction between rat serum phosphorylcholine binding protein and platelet activating factor

The binding of rat serum phosphorylcholine binding protein (PCBP) to platelet activating factor (PAF) has been demonstrated using a HPLC-gel filtration technique. The bulk of the bound [3H]-PAF eluted with a higher molecular weight species of PCBP, possibly an aggregated form of PCBP. A smaller amount of [3H]-PAF co-eluted with the major monomeric species of PCBP. Formation of the PCBP-PAF complex was calcium dependent and could be inhibited by phosphorylcholine, suggesting the involvement of the phosphorylcholine binding site on PCBP. Binding of albumin and alpha 1-acid glycoprotein to PAF was not affected by phosphorylcholine or calcium. The specificity of this binding may explain the inhibitory effect of PCBP and related phosphorylcholine binding proteins on PAF induced aggregation of platelets.     

Interaction between alpha 1 and beta 1 subunits of human hemoglobin

We prepared normal and modified alpha and beta globulin chains in which C-terminal residues were enzymatically removed. The CD spectra of the deoxy form of these chains and the reconstituted modified Hb's were measured in the Soret region. The CD spectra of the modified Hb's were markedly different from the arithmetic means of respective spectra of their constituent chains. This difference was ascribed to the interaction between alpha 1 and beta 1 subunits to make the alpha 1 beta 1 dimer. The peak wavelength of the difference CD spectra could be classified into two groups, one was 433 +/- 1 nm and the other 437 +/- 1 nm. A comparison of this classification with the previously identified quaternary structures revealed that the R and T structures showed a maximum of the difference CD spectra at 437 +/- 1 nm and 433 +/- 1 nm, respectively. These results indicated that the R and T structures differed in the interaction between alpha 1 and beta 1 subunits.     

Interaction between isolated cytochrome c1 and cytochrome c

Cytochrome c1 from bovine heart mitochondria was isolated by a modification of the technique of K?nig et al. [(1980) Biochim. Biophys. Acta 621, 283-295] which involved an affinity chromatography step on a gel with yeast cytochrome c as a ligand. Its spectra, electrophoretic pattern in presence of sodium dodecylsulfate, its reducibility by ascorbate and cytochrome c were characteristic of a native cytochrome, with a single polypeptide having an apparent molecular weight of 30 000. By using an arylazido derivative of cytochrome c, having the photoactive group bound to lysine 13, upon illumination a cross-link with the described preparation of cytochrome c1 was obtained. By pepsin digestion of the cross-linked complex a limiting fragment was obtained and partially sequenced. It allowed to identify the site of binding of cytochrome c near the sequence 167-174 of cytochrome c1.     

酪氨酸激酶Jak3与核小体组装蛋白Nap1的相互作用

在白细胞介素－２（ｉｎｔｅｒｌｅｕｋｉｎ－２,ＩＬ－２）的信号转导过程中,酪氨酸激酶Ｊａｋ３起着至关重要的作用。它不但参与Ｊａｋ－Ｓｔａｔ通路的传递,而且通过与一些未知的信号分子相互作用调节一些原癌基因的表达,如ｃ－ｆｏｓ,ｃ－ｍｙｃ等。由于目前越来越多的证据表明在信号转导过程中两个蛋白质之间的相互作用需要磷酸酪氨酸的存在,为此构建了酪氨酸磷酸化相关原酵母双杂交系统,以进一步阐释Ｊａｋ３在ＩＬ－２     

Interaction between heme oxygenase-1 and -2 proteins

The three isoforms of heme oxygenase (HO), the rate-limiting enzyme in heme degradation, are the products of different genes that show marked differences in regulation and expression. Why is there redundancy in the heme degradation pathway, and why are there differences in tissue expression of HO isoenzymes are unanswered questions? An interaction between HO-1 and HO-2 is suspected by the co-localization of these enzymes in the lung and regions of the brain. Using multiple models and assays, we demonstrated an interaction between HO-1 and HO-2 at amino acids 0-45 of HO-2 and amino acids 58-80 of HO-1. The latter corresponds to a highly conserved, hydrophilic, and exposed region of the protein. Furthermore, the observed activity of the HO-1.HO-2 complex was lower than that expected from the sum of HO-1- and HO-2-derived activities, suggesting that this interaction serves to limit HO enzymatic activity. We speculate that this HO-1.HO-2 protein interaction may promote non-enzymatic functions of HO.     

Interaction of oxyanions with thioredoxin-activated chloroplast coupling factor 1

Interaction between F(1)-ATPase activity stimulating oxyanions and noncatalytic sites of coupling factor CF(1) was studied. Carbonate, borate and sulfite anions were shown to inhibit tight binding of [14C]ATP and [14C]ADP to CF(1) noncatalytic sites. The demonstrated change of their inhibitory efficiency in carbonate-borate-sulfite order coincides with the previously found change in efficiency of these anions as stimulators of CF(1)-ATPase activity [Biochemistry (Mosc.) 43 (1978) 1206-1211]. Inhibition of tight nucleotide binding to noncatalytic sites was accompanied by stimulation of nucleotide binding to catalytic sites. This suggests that stimulation of CF(1)-ATPase activity is caused by interaction between oxyanions and noncatalytic sites. A most efficient stimulator of CF(1)-ATPase activity, sulfite oxyanion, appeared to be a competitive inhibitor with respect to ATP and a partial noncompetitive inhibitor with respect to ADP. The inhibition weakened with increasing time of CF(1) incubation with sulfite and nucleotides. Sulfite is believed to inhibit fast reversible interaction between nucleotides and noncatalytic sites and to produce no effect on subsequent tight binding of nucleotides. A possible mechanism of the oxyanion-stimulating effect is discussed.     

Interaction between initiator Met-tRNAfMet and elongation factor EF-Tu from E. coli

It has recently been shown that the non-formylated initiator Met-tRNAfMet from E. coli can form a stable ternary complex with the elongation factor EF-Tu and GTP. Using the protection of EF-Tu:GTP against spontaneous hydrolysis of the aminoacylester bond of Met-tRNAfMet, we confirm these results, and show that the protection is specific for the non-formylated form of the initiator tRNA. The ternary complex Met-tRNAfMet:EF-Tu:GTP can be isolated by column chromatography in a way similar to that demonstrated previously with EF-Tu complexed to the elongator Met-tRNAmMet. 32P-labeled Met-tRNAfMet within the ternary complex was analyzed by the footprinting technique. The pattern of initiator tRNA protection by EF-Tu against ribonuclease digestion is not significantly different from the one found previously for elongator tRNAs. These results lead us to suggest that the initiator tRNAfMet, under growth conditions which do not permit formylation, may to some extent function as an elongator tRNA.     

Interaction between plasminogen activator inhibitor type-2 and pre-mRNA processing factor 8

Plasminogen activator inhibitor type-2 (PAI-2), a mem-ber of the ovalbunin family of serine protease inhibitor (ov-serpin) super family, is a multifunctional protein which isinvolved in the regulation of fibrinolysis, invasion andmetastasis of cancer cells, and regulation of apoptosis. HeLacells transfected with PAI-2 were protected from TNF-α-induced apoptosis. Like other members of ov-serpin family,PAI-2 contains a non-conserved 33 amino acid residuesloop region between its C and D he…     

Interaction between geminivirus replication protein and the SUMO-conjugating enzyme is required for viral infection

Geminiviruses are small DNA viruses that replicate in nuclei of infected plant cells by using plant DNA polymerases. These viruses encode a protein designated AL1, Rep, or AC1 that is essential for viral replication. AL1 is an oligomeric protein that binds to double-stranded DNA, catalyzes the cleavage and ligation of single-stranded DNA, and induces the accumulation of host replication machinery. It also interacts with several host proteins, including the cell cycle regulator retinoblastoma-related protein (RBR), the DNA replication protein PCNA (proliferating cellular nuclear antigen), and the sumoylation enzyme that conjugates SUMO to target proteins (SUMO-conjugating enzyme [SCE1]). The SCE1-binding motif was mapped by deletion to a region encompassing AL1 amino acids 85 to 114. Alanine mutagenesis of lysine residues in the binding region either reduced or eliminated the interaction with SCE1, but no defects were observed for other AL1 functions, such as oligomerization, DNA binding, DNA cleavage, and interaction with AL3 or RBR. The lysine mutations reduced or abolished virus infectivity in plants and viral DNA accumulation in transient-replication assays, suggesting that the AL1-SCE1 interaction is required for viral DNA replication. Ectopic AL1 expression did not result in broad changes in the sumoylation pattern of plant cells, but specific changes were detected, indicating that AL1 modifies the sumoylation state of selected host proteins. These results established the importance of AL1-SCE1 interactions during geminivirus infection of plants and suggested that AL1 alters the sumoylation of selected host factors to create an environment suitable for viral infection.