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Query: CAS:56-41-7 (alanine)
 70,945 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The lambdoid bacteriophage regulate gene expression by suppressing transcription terminators. Although similar in sequence to lambda, HK022 lacks an analogue to the lambda N antitermination gene and a distinct nutR sequence. To define the HK022 antitermination system, we plated the phage on Escherichia coli nus mutants that inhibit lambda N function. Only rpoB60 (also called nusC60) blocked HK022 lytic growth. Analyses of HK022-lambda hybrid phage suggested that a HK022 function analogous to lambda Q was inhibited by rpoB60. This result was confirmed with pR'-tR'-galK fusions. HK022 Q-protein suppressed tR' in wild-type but not in rpoB60 mutants. The lambda Q-protein, although inhibited by rpoB60, was more active than the HK022 analogue. A single amino acid difference between the two Q-proteins accounts for the phenotype. Changing the penultimate residue of HK022 Q from alanine to the lambda threonine generated a phage that could propagate on rpoB60 hosts. Host and phage mutations that permitted HK022 growth in rpoB60 strains were characterized. The bacterial suppressors were located in the Escherichia coli nusB gene. The phage suppressors represented recessive mutations in a HK022 b-region sequence encoding an open reading frame of 73 codons.
J Mol Biol 1992 Sep 05
PMID:The Escherichia coli rpoB60 mutation blocks antitermination by coliphage HK022 Q-function. 152 93

Important mammalian defensive functions such as phagocytosis are triggered in leukocytes by the interaction of the Fc region of IgG with cell surface receptors (Fc gamma R). The CH2 domain of IgG has been implicated previously as the site of interaction with human and mouse Fc gamma R. This domain was mapped for interaction with mouse Fc gamma R11 expressed by the macrophage-like cell line P388D1, using two panels of a total of 32 site-directed mutants of mouse IgG2b and chimeric human IgG3 monoclonal antibodies. Two potential binding sites have been identified: one in or within the vicinity of the lower hinge site on IgG for human Fc gamma R1, and one within the binding site on IgG for Clq. The three mutant IgGs (Gly 237----Ala, Asn 297----Ala, and Glu 318----Ala) which do not interact in complexed form also fail to bind as monomers. A 1H NMR study of the three non-binding monomeric mutants suggests that the mutations are largely site-specific, indicating that IgG interacts with mouse Fc gamma R11 at two regions within the CH2 domain. This interaction dictates phagocytosis mediated by Fc gamma R11 of the P388D1 cell line.
Mol Immunol 1992 Jan
PMID:Multiple binding sites on the CH2 domain of IgG for mouse Fc gamma R11. 153 Sep 84

Phosphorylation of p34cdc2 can both positively and negatively regulate its kinase activity. We have mapped two phosphorylation sites in Xenopus p34cdc2 to Thr-14 and Tyr-15 within the putative ATP-binding region of p34cdc2. Mutation of these sites to Ala-14 and Phe-15 has no effect on the final histone H1 kinase activity of the cyclin/p34cdc2 complex. Phosphopeptide analysis shows that there is at least one more site of phosphorylation on p34cdc2. When Thr-161 is changed to Ala, two phosphopeptide spots disappear and it is no longer possible to activate the H1 kinase activity of p34cdc2. We suggest that Thr-161 is a third site of phosphorylation, which is required for kinase activity. All three phosphorylations are induced by cyclin. None of the phosphorylations appears to be required for binding to cyclin, as indicated by the ability of the triple mutant, Ala-14, Phe-15, Ala-161, to bind cyclin. The activating phosphorylation that requires Thr- or Ser-161 occurs even in a catalytically inactive K33R mutant of p34cdc2 and hence does not appear to be the result of intramolecular autophosphorylation. We have detected an activity in Xenopus extracts required for activation of p34cdc2 and present evidence that this is a p34cdc2 activating kinase which, in a cyclin-dependent manner, probably directly phosphorylates Thr-161.
Mol Biol Cell 1992 Jan
PMID:Role of phosphorylation in p34cdc2 activation: identification of an activating kinase. 153 35

A novel mutation, FruS localised in the fru operon was obtained. It uncouples expression of the genes determining synthesis of the fructose-specific transport proteins and fructose-1-phosphate kinase. In FruS bacteria the fruA and fruF genes (coding for Enzyme IIfru and FPr, respectively) are constitutive by expressed while fruK (encoding fructose-1-phosphate kinase) remains inducible. In contrast to other mutations, which render expression of the whole fru operon constitutive, the FruS mutation: (1) does not lead to D-xylitol sensitivity; (2) does not inhibit growth on D-lactate, pyruvate and L-alanine; (3) does not decrease phosphoenolpyruvate (PEP) synthase activity.
Mol Gen Genet 1992 Apr
PMID:A novel mutation FruS, altering synthesis of components of the phosphoenolpyruvate: fructose phosphotransferase system in Escherichia coli K12. 153 39

Residue Glu152 of tyrosyl-tRNA synthetase (TyrTS) from Bacillus stearothermophilus is close to phosphate groups 73 and 74 of tRNATyr in the structural model of their complex. TyrTS(E152A), a mutant synthetase carrying the change of Glu152 to Ala, was toxic when overproduced in Escherichia coli. The toxicity strongly increased with the growth temperature. It was measured by the ratios of the efficiencies with which the producing cells plated in induced or repressed conditions and at 30 degrees C or 37 degrees C. TyrTS(E152Q), TyrTS(E152D) and the wild-type synthetase were not toxic in conditions where TyrTS(E152A) was toxic. The toxicity of TyrTS(E152A) was abolished by additional mutations of the synthetase that prevent the binding of tRNATyr but not by a mutation that prevents the formation of Tyr-AMP. Because TyrTS(E152A) was active for the aminoacylation of tRNATyr, its toxicity could only be due to faulty interactions with non-cognate tRNAs, either their non-productive binding or their mischarging with tyrosine. TyrTS(E152A) and TyrTS(E152Q) mischarged tRNAPhe and tRNAVal in vitro with tyrosine unlike TyrTS(E152D) or the wild-type enzyme. Thus, several features of the side-chain in position 152 of TyrTS, including its negative charge, are important for the rejection of non-cognate tRNAs. TyrTS(E152A), TyrTS(E152D) and TyrTS(E152Q) had similar steady-state kinetics parameters for the charging of tRNATyr with tyrosine in vitro, with kcat/KM ratios improved 2.5 times relative to the wild-type synthetase. We conclude that the side-chain of residue Glu152 weakens the binding of TyrTS to tRNATyr and prevents its interaction with non-cognate tRNAs.
J Mol Biol 1992 Feb 05
PMID:Role of residue Glu152 in the discrimination between transfer RNAs by tyrosyl-tRNA synthetase from Bacillus stearothermophilus. 154 20

The serum half-lives of a wild-type recombinant mouse monoclonal antibody of the IgG2b isotype and a mutant antibody differing from the wild-type antibody by a single amino acid substitution introduced into the CH2 domain, the replacement of Asn 297 by Ala to delete the conserved site of heavy chain glycosylation, were determined in the rat. The biological half-life of the aglycosyl Asn 297-Ala mutant recombinant antibody (4.8 days) was significantly shorter than that of the normally glycosylated wild-type antibody (7.4 days) by enzyme immunoassay. A similar difference between the biological half-lives of 125I-labelled aglycosyl and wild-type antibodies (2.9 and 4.0 days, respectively) was determined by gamma counting. Analysis of serum samples demonstrated that both recombinant antibodies were present in the circulation predominantly as intact monomeric IgG and revealed no differences that could account for the more rapid elimination of the aglycosyl antibody. The results of this investigation indicate that the carbohydrate residues contribute only in part to the survival of IgG in vivo and suggest that the diminished half-life of the aglycosyl antibody is due to increased catabolism in the extravascular tissues.
Mol Immunol 1992 Feb
PMID:Blood clearance in the rat of a recombinant mouse monoclonal antibody lacking the N-linked oligosaccharide side chains of the CH2 domains. 154 98

The serum half-lives of three recombinant mouse monoclonal antibodies, differing radically in their ability to bind to Clq or FcRI but only minimally in structure, were determined in the BALB/c mouse following intravenous administration. The wild-type antibody, a chimaeric antibody comprising variable domains binding 3-iodo-4-hydroxy-5-nitrophenylacetate and constant domains of the mouse IgG2b isotype, was eliminated from the bloodstream with biphasic kinetics: alpha-phase, 0.5 days; beta-phase, 7.0 days. The alpha- and beta-phase half-lives of mutant recombinant antibodies with single amino acid substitutions, either Glu 235-Leu allowing binding to the mouse FcRI, or Lys 322-Ala reducing Clq binding 30-fold, were indistinguishable from those of the wild-type antibody demonstrating that the biological half-life of intact mouse IgG is independent of the ability to bind Clq or FcRI. The major implication of the present study is that IgG molecules which have been genetically engineered to eliminate interaction with other components of the immune system should retain the long half-life typical of natural antibodies.
Mol Immunol 1992 Feb
PMID:Recombinant mouse monoclonal antibodies with single amino acid substitutions affecting Clq and high affinity Fc receptor binding have identical serum half-lives in the BALB/c mouse. 154 99

We have studied the phosphorylation of the nuclear oncoprotein Fos by cyclic AMP-dependent protein kinase (PKA). We demonstrate that the human c-Fos protein, phosphorylated either in vitro with purified PKA or in vivo in JEG3 cells following treatment with forskolin, has similar phosphotryptic peptide maps. Serine 362, which constitutes part of a canonical PKA phosphorylation site (RKGSSS), is phosphorylated both in vivo and in vitro. A mutant of Fos protein in which serine residues 362 to 364 have been altered to alanine residues is not efficiently phosphorylated in vitro. Furthermore, Fos protein in which serines 362 to 364 have been altered to alanine shows increased transforming potential. We propose that phosphorylation of Fos by PKA is an important regulatory step in controlling its activity in normal cell growth and differentiation.
Mol Cell Biol 1992 Mar
PMID:Alteration of a cyclic AMP-dependent protein kinase phosphorylation site in the c-Fos protein augments its transforming potential. 154 28

Using homopolymeric units of either phenylalanine or tryptophan to replace the natural core segment of the Escherichia coli alkaline phosphatase signal peptide, the hydrophobicity requirements for protein export and processing were further explored. The mutant signal peptide containing polyphenylalanine functioned at least as efficiently as the wild-type, while the signal incorporating polytryptophan was dysfunctional. The transport properties of these mutants confirm our work with sequences rich in aliphatic residues; namely that a high mean hydrophobicity per residue is critical for complete and rapid precursor processing and for translocation of the protein. The efficient transport properties of the polyphenylalanine-containing signal peptide demonstrate that neither the bulky, aromatic nature of phenylalanine nor the unusually high hydrophobicity of this mutant peptide adversely alters function. This study also suggests that the low occurrence of phenylalanine in natural signal sequences is not of functional consequence but probably reflects the low number of DNA codons for this residue. The polytryptophan-containing precursor was membrane inserted but not translocated. This type of transport defect suggests that this is a weakly hydrophobic signal peptide, consistent with hydropathy scales, which indicate that tryptophan is comparable to alanine. This application of polymeric sequences provides a function-based assay for the evaluation of amino acid hydrophobicity.
J Mol Biol 1992 Mar 05
PMID:Signal sequences containing multiple aromatic residues. 154 10

RNA metabolism plays a central role in cell growth. It is essential to regulate RNA synthesis, processing, stability and degradation. Conformational changes in RNA are key elements in regulating cellular processes. Recently, an increasing number of putative RNA helicases from different organisms ranging from Escherichia coli to humans and viruses have been identified. They are involved in diverse cellular functions such as RNA splicing, ribosome assembly, initiation of translation, spermatogenesis, embryogenesis, and cell growth and division. Based on sequence homologies these proteins were grouped in a family, the D-E-A-D box protein family (D-E-A-D = Asp-Glu-Ala-Asp). Some of the better characterized members have been shown to possess ATP-binding and hydrolysing activities as well as ATP-dependent RNA helicase activities. Most of the genes encoding such proteins have been isolated from yeast, on which we will focus in this review. From sequence data, three of the members form a subfamily, the D-E-A-H subfamily.
Mol Microbiol 1992 Feb
PMID:D-E-A-D protein family of putative RNA helicases. 155 44


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