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M De Felice

Publications and source records attributed to M De Felice.

At least 73 records · Page 4Linked to original sources
PubMed1985

Regulatory role of a monomorphic determinant of HLA Class I antigens in T cell proliferation.

The role of HLA Class I antigens in T cell proliferation was investigated by using the anti-HLA Class I monoclonal antibodies (MoAb) CR10-215, CR10-325, and CR11-115. MoAb CR10-215 and CR11-115 recognize the same (or spatially close) monomorphic determinant, which is distinct and spatially distant from that reacting with MoAb CR10-325. Addition of MoAb CR10-215 and CR11-115 to cultures of peripheral blood mononuclear cells stimulated with MoAb OKT3, MoAb Pan T2, PHA, or PPD inhibited cell proliferation. The blocking is specific in that the anti-HLA Class I MoAb CR10-325 and the Pan T MoAb Pan T1 had no effect on the proliferation. The inhibitory activity of MoAb CR10-215 and CR11-115 does not reflect i) toxic effects, ii) induction of suppressor cells and factors, iii) blocking of the binding of mitogens to lymphocytes, iv) inhibition of the production of interleukin 1 (IL 1) and interleukin 2 (IL 2), or v) function of IL 2 receptor. Anti-HLA Class I MoAb were able to inhibit the proliferation of purified, Tac-, T cells. The inhibited cells did not express Tac antigen, as assayed by direct immunofluorescence, with MoAb anti-Tac, but released a normal amount of IL 2 in culture medium. These results indicate that monomorphic determinants of the HLA Class I complex are involved in the regulation of T cell proliferation. The effect appears to occur at the level of IL 2 receptor expression.

Antibodies, Monoclonal↗
PubMed1983

Molecular structure of ilvIH and its evolutionary relationship to ilvG in Escherichia coli K12.

ilvIH of Escherichia coli K12 codes for a valine-sensitive acetohydroxy acid synthase (AHASIII). The DNA sequence of ilvIH was determined. Open reading frames and appropriate translation signals exist for two polypeptides, one containing 565 amino acids (ilvI polypeptide) and the other 160 amino acids (ilvH polypeptide). A graphic matrix analysis shows three clearcut regions of homology between ilvI and ilvG (codes for AHASII). Within these three regions of homology, 50-60% of the amino acid sequences of AHASII and AHASIII are conserved. Inspection of the region between ilvG and ilvE (the K region) revealed that it can potentially code for an 86 amino acid polypeptide. A computer analysis shows small but significant homology between the predicted amino acid sequences of the N-terminal half of the ilvH polypeptide and the putative region K polypeptide. We conclude that ilvIH and ilvG-region K evolved from a common ancestor.

Acetolactate Synthase↗
PubMed1983

IlvHI locus of Salmonella typhimurium.

In Escherichia coli K-12, the ilvHI locus codes for one of two acetohydroxy acid synthase isoenzymes. A region of the Salmonella typhimurium genome adjacent to the leucine operon was cloned on plasmid pBR322, yielding plasmids pCV47 and pCV49 (a shortened version of pCV47). This region contains DNA homologous to the E. coli ilvHI locus, as judged by hybridization experiments. Plasmid pCV47 did not confer isoleucine-valine prototrophy upon either E. coli or S. typhimurium strains lacking acetohydroxy acid synthase activity, suggesting that S. typhimurium lacks a functional ilvHI locus. However, isoleucine-valine prototrophs were readily isolated from such strains after mutagenesis with nitrosoguanidine. In one case we found that the Ilv+ phenotype resulted from an alteration in bacterial DNA on the plasmid (new plasmid designated pCV50). Furthermore, a new acetohydroxy acid synthase activity was observed in Ilv+ revertants; this enzyme was similar to E. coli acetohydroxy acid synthase III in its lack of activity at low pH. This new activity was correlated with the appearance in minicells of a new polypeptide having an approximate molecular weight of 61,000. Strains carrying either pCV49 or pCV50 produced a substantial amount of ilvHI-specific mRNA. These results, together with results from other laboratories, suggest that S. typhimurium has functional ilvB and ilvG genes and a cryptic ilvHI locus. E. coli K-12, on the other hand, has functional ilvB and ilvHI genes and a cryptic ilvG locus.

Acetolactate Synthase↗
PubMed1982

Strong association between an HLA-DR antigen and thyroid carcinoma.

A group of 20 patients affected with thyroid carcinoma, all from Southern Italy, was typed for HLA-A, -B, -C and -DR antigens. Sixteen of them (80%) typed for DR1, while in the control group (120 unrelated healthy individuals from the same region) only 22 (18.3%) shared the same antigen (chi 2 = 32.96). The data indicate a highly significant association between the HLA-DR1 gene and the thyroid carcinoma.

Adenocarcinoma↗
PubMed1981

Acetohydroxy acid synthase isoenzymes of Escherichia coli K-12: a trans-acting regulatory locus of ilvHI gene expression.

We isolated an Escherichia coli K-12 regulatory mutation affecting the acetohydroxy acid synthase III isoenzyme. This mutation was found to lie outside the structural genes ilvHI for this isoenzyme and was designated lrs-1. A strain carrying this mutation was found to be altered in the leucine-mediated control of ilvHI mRNA and acetohydroxy acid synthase III synthesis observed in the isogenic lrs+ strain. These alterations appeared to be a consequence of a reduced intracellular concentration of a single one of five tRNALeu isoaccepting species.

Acetolactate Synthase↗
PubMed1981

Cryptic operon for beta-glucoside metabolism in Escherichia coli K12: genetic evidence for a regulatory protein.

Escherichia coli K12 does not metabolize beta-glucosides such as arbutin and salicin because of lack of expression of the bglBSRC operon, which contains structural genes for transport (bglC) and hydrolysis (bglB) of phospho-beta-glucosides. Mutants carrying lesions in the cis-acting regulatory site bglR metabolize beta-glucosides as a consequence of expression of this cryptic operon (Prasad and Schaefler 1974). We isolated mutations promoting beta-glucoside metabolism that were unlinked to bglR; some of these mutations were shown to be amber. All of them were mapped at 27 min on the E. coli K12 linkage map and appeared to define a single gene, for which we propose the designation bglY. Utilization of beta-glucosides in bglY mutants appeared to be a consequence of expression of the bglBSRC operon, since bglB bglR and bglB bglY double mutants had the same phenotype. All bglY mutations analyzed were recessive to the wild-type bglY+ allele. Phospho-beta-glucosidase B and beta-glucoside transport activities are inducible in bglY mutants, as they are in bglR mutants. Metabolism of beta-glucosides in both bglR and bglY mutants required cyclic AMP. We propose that bglY encodes a protein acting as a repressor of the bglBSRC operon, active in both the presence and absence of beta-glucosides, whose recognition site would be within the bglR locus.

Carrier Proteins↗
PubMed1981

A role for threonine deaminase in the regulation of alpha-acetolactate biosynthesis in Escherichia coli K12.

The flow of carbon to alpha-acetolactate is Escherichia coli K12 is shown to involve the endogenous pool of alpha-ketobutyrate (alpha-KB). In vivo, the acetohydroxy acid synthase (AHAS) isoenzymes have an affinity for alpha-KB sufficiently high that alpha-acetolactate production is severely limited when alpha K-B is supplied exogenously. The ability of threonine deaminase to make alpha-KB is correlated with the synthesis of the AHAS isoenzymes. Mutations in ilvA that alter the catalytic and allosteric properties of threonine deaminase affect alpha-KB production and the expression of the AHAS isoenzymes in a direct way. The ilv A538 mutation results in a feedback-hypersensitive threonine deaminase ans slow alpha-KB and AHAS production. A spontaneous revertant of an ilvA538 strain expressing a feedback-resistant threonine deaminase produces alpha-KB and AHAS more quickly. A physiological role for the activator (valine) site on threonine deaminase is proposed and valine is shown to increase alpha-KB production in vivo. Valine can thus regulate its own biosynthetic pathway without jeopardizing the production of isoleucine. The physiological implications of the role of alpha-KB in the biosynthesis of acetolactate are discussed.

Acetolactate Synthase↗
PubMed1981

Physical characterization of the ilvHI operon of Escherichia coli K-12.

The ilvHI and leu genes of Escherichia coli K-12 are contained on a single 10.9-kilobase EcoRI fragment of deoxyribonucleic acid derived from the leu transducing phage lambda G4. Since the expression of all of these genes is controlled by leucine, we investigated whether they are part of single operon or whether they constitute separate but adjacent operons controlled from a common site. Both cloning and hybridization studies indicated that ilvHI and leu are distinct operons. They are transcribed in opposite directions and are separated by approximately 1,500 base pairs of deoxyribonucleic acid. Hybridization experiments showed that the expression of ilvHI is regulated chiefly at the level of transcription. The size of the ilvHI messenger ribonucleic acid is estimated to be 2,550 bases.

Acetolactate Synthase↗
PubMed1980

The HLA system in the Campania region: a genetic study.

The HLA-A, -B and -C locus gene frequencies and the significant A, B and B, C haplotypes of the population of Campania (Southern Italy) are reported. From a comparison of gene frequencies and from an overall genetic distance evaluation with other European and Mediterranean populations the typical Mediterranean structure of the Campanian population is confirmed. While keeping several Middle Eastern features, it places itself as far from Northern Italy (Bergamo) as from the Spanish and the French populations. Among all the groups compared, including Turkish and Lebanese, the largest distance is measured from the English, the Danish and the German populations.

Chromosome Mapping↗
PubMed1977

Growth inhibition of Escherichia coli K-12 by L-valine: a consequence of a regulatory pattern.

We studied the production of the ilvG gene product, the valine resistant acetolactate synthase isoenzyme II, in an ilvO+ G+ ilvB ilvHI derivative of Escherichia coli K-12. This strain contains mutations in the structural genes for the valine sensitive acetolactate synthase isoenzymes I and III. We find that the ilvG gene is not expressed in this strain when gworn with either isoleucine and valine or with isoleucine, leucine and valine, or when limited for either isoleucine or valine. Since we previously found that the ilvG gene is expressed in an ilvO603 containing strain (Favre et al., 1976), we presume that the mechanism by which E. coli K-12 regulates the ilv gene cluster is responsible for the lack of ilvG expression in the ilvO+ strain. The valine sensitivity of E. Coli K-12 is a consequence of this regulatory pattern.

Acetolactate Synthase↗
PubMed1974

Multiplicity of isoleucine, leucine, and valine transport systems in Escherichia coli K-12.

The kinetics of isoleucine, leucine, and valine transport in Escherichia coli K-12 has been analyzed as a function of substrate concentration. Such analysis permits an operational definition of several transport systems having different affinities for their substrates. The identification of these transport systems was made possible by experiments on specific mutants whose isolation and characterization is described elsewhere. The transport process with highest affinity was called the "very-high-affinity"process. Isoleucine, leucine, and valine are substrates of this transport process and their apparent K(m) values are either 10(-8), 2 x 10(-8), or 10(-7) M, respectively. Methionine, threonine, and alanine inhibit this transport process, probably because they are also substrates. The very-high-affinity transport process is absent when bacteria are grown in the presence of methionine, and this is due to a specific repression. Methionine and alanine were also found to affect the pool size of isoleucine and valine. Another transport process is the "high-affinity" process. Isoleucine, leucine, and valine are substrates of this transport process, and their apparent K(m) value is 2 x 10(-6) M for all three. Methionine and alanine cause very little or no inhibition, whereas threonine appears to be a weak inhibitor. Several structural analogues of the branched-chain amino acids inhibit the very-high-affinity or the high-affinity transport process in a specific way, and this confirms their existence as two separate entities. Three different "low-affinity" transport processes, each specific for either isoleucine or leucine or valine, show apparent K(m) values of 0.5 x 10(-4) M. These transport processes show a very high substrate specificity since no inhibitor was found among other amino acids or among many branched-chain amino acid precursors or analogues tried. The evolutionary significance of the observed redundancy of transport systems is discussed.

Alanine↗