Biomedical subjects

E Sala

Publications and source records attributed to E Sala.

At least 91 records · Page 5Linked to original sources

PubMed1986

Transcription and expression of zein sequences in yeast under natural plant or yeast promoters.

Maize genomic fragments containing the regulatory and coding regions of a zein gene for a low size class 23-kd protein have been inserted in an interspecific Escherichia coli-Saccharomyces cerevisiae expression vector in different constructions. The presence of the inducible GAL1-10 upstream activation site (UAS) allows us to regulate differentially by carbon sources the transcription of the zein gene both under the plant promoter and under the yeast CYC-1 promoter. We found that the zein promoter region is properly recognized at the correct transcription start, while different termination points occur during transcription. The yeast UAS was also shown to function as a typical eukaryotic enhancer regardless of its distance or orientation with respect to the plant promoter. Yeast cells transformed by a plasmid containing a zein sequence fused to a short piece of the CYC-1 gene produced a fused polypeptide, of expected mol. wt, in variable amount from 0.2 to 5% depending on the growth phase conditions.

Journal Article↗

PubMed1986

Monoclonal radioimmunoassay for hepatitis B surface antigen in sera of children with acute leukemia.

Hepatitis B surface antigen (HBsAg) was detected by a monoclonal antibody radioimmunoassay in sera from five of 43 children (11.6%) with acute leukemia, who were negative by conventional assay. None of the nine positive sera had evidence of reactivity for HBV-DNA or DNA-polymerase activity. No correlation was found between the presence of HBsAg in serum by monoclonal RIA and the behaviour of anti-viral antibodies. Twenty-two children could be studied for liver HBsAg by immunofluorescence, and nine of them (40.9%) were positive, including three patients having HBsAg reactivity in serum. These data indicate that monoclonal antibodies increase the sensitivity of RIA for the detection of serum HBsAg in children with acute leukemia, who previously have frequently been found to have an atypical hepatitis B virus (HBV) serology.

Acute Disease↗

PubMed1985

Each zein gene class can produce polypeptides of different sizes.

The family of zein proteins in maize consists of several prototypes whose amino sequence is characterized by a repetitive block structure. We have now isolated and characterized a new series of zein cDNA clones from a cDNA library made from protein-body polysomal mRNA. The nucleotide sequences and the hybrid-selected translation results indicate that anomalous zein genes with termination codons within the coding region are transcribed, translated and possibly accumulated into zein protein bodies. The sequence analysis of these new clones and their comparison with already characterized zein sequences, all from the same maize line, indicate a large variability in the amino acid sequence of the blocks both among the prototypes and within members of each prototype. Northern blot analysis of total RNA from endosperms at different maturation stages shows a differential expression of each prototype sequence with the production, within each family, of zein transcripts coding for discrete size classes of polypeptides. The results allow a better definition of the zein system, clarify the relationship between sequence types and polypeptide size classes, and suggest the possibility of inserting lysine codons to raise the nutritional value of the seed storage protein.

Journal Article↗

PubMed1982

Multiplicity and diversity of cloned zein cDNA sequences and their chromosomal localisation.

We have constructed and screened cDNA libraries from total maize endosperm poly(A) RNA or from a mRNA fraction enriched in zein sequences. From these libraries we have isolated clones representative of the major classes of zein cDNA sequences and have characterised them by crosshybridisation, by hybrid-selected translation, by in situ hybridisation to maize chromosomes, and hybridisation to genomic Southern blots. We conclude that at least four types of non cross-hybridising zein sequences are present, two coding for light chains and two for heavy chains. At least in the case of the light zeins, there is considerable sequence diversity among the clones which hybridise to each type. Similar results are obtained by translation of the mRNAs selected by each clone. In situ hybridisation shows that the light chain zein genes are located on chromosomes 4, 7, and 10, whilst genes coding for some of the heavy chain zeins are confined to the distal part of the long arm of chromosome 4.

Journal Article↗

PubMed1979

Genes and mRNAs coding for zein polypeptides in Zea mays.

Zein messenger RNAs from maize endosperm were purified by successive oligo(dT)-cellulose chromatography and sucrose gradient centrifugation. Polyacrylamide gel electrophoresis under denaturing conditions revealed the presence of two size classes of zein messenger RNAs of Mr 3.5 x 10(5) and 4.10 x 10(5). The mRNA was shown to synthesize the major zein polypeptides, to have a base composition characteristic of a poly(A)-containing RNA and to be transcribed by reverse transcriptase into complementary DNA. The r0t1/2 of the hybridization curve of cDNA hybridized to an excess of mRNA was shown to be 7 x 10(-2) M . s indicating that about 15 non-cross-hybridizing sequences are present in the zein mRNA preparations. The kinetics of cDNA annealing with an excess of maize DNA from 2 n cells suggest a ten-times reiteration of each mRNA sequence. This result is confirmed from saturation experiments, where in cDNA excess to DNA, the number of zein genes per haploid maize genome was estimated as about 120 copies. Similar experiments carried out on DNA from normal and mutant endosperms (3n cells) indicate the absence of large amplifications or deletions of zein genes in the tissue devoted to zein synthesis.

DNA↗

PubMed1975

13C-nuclear magnetic resonance studies of 85% 13C-enriched amino acids and small peptides. pH effects on the chemical shifts, coupling constants, kinetics of cis-trans isomerisation and conformation aspects.

The 13C chemical shifts of several 85% 13C-enriched amino acids and small peptides were studied as a function of pH. The results show that the chemical shifts of carbon atoms of ionizable groups vary significantly within the zone of their pK. Generally with the pH GOING FROM 7 to 1 all the deltaC are shifted more or less upfield with the exception of the carbonyl group carbon of the second last residue which is shifted slightly downfield. This suggests the formation of an hydrogen bond at acid pH involving in a seven-membered ring the C=O in question and the COOH terminal. The percentage of cis and trans conformers of glycyl-L-proline and glycyl-L-prolylglycine were studied as a function of pH. The trans form is always preponderant whatever the pH. The accessibility of the carbonyl group to protonation of the proline residue strongly influences the cis-trans equilibrium. Thus, with the pH varying from 7 to 1, the trans isomer changes from 61 to 85% for glycyl-L-proline and only from 77 to 80% for glycyl-L-prolylglycine. The proton NMR studies underline the important differences existing between the two molecular forms of glycyl-L-proline. The cis conformation is characterized with regard to the trans form by the non-equivalence of the alpha-protons of the glycine residue, by a lower pK(1) and by a larger deltadeltaHalpha of the proline residue as a function of pH. These results could suggest an end-to-end interaction in the cis form of the glycyl-L-proline molecule. The 13C-13C coupling constants were also studied as a function of pH. The results show that J(Co-Calpha) of a C-terminal residue, varying from 5 to 6 Hz and reflecting thhe pK of the carboxylate group, is a linear function of delta(Co) and delta(Calpha) as in the case of the amino acids. The total variation of the electron density of those two carbons in an amino acid is approximately 40% weaker than in a C-terminal residue. The charge distribution along the Calpha-C(o) bond, however, is practically the same in both cases. Finally the ratios of the conversion rate constants of the two isomers cis-trans of glycyl-proline were calculated at different pH values; the relations between the isomer percentages and delta(Co), delta(Calpha) on the one hand and the J(Co-Calpha) on the other were established.

Amino Acids↗

PubMed1975