Biomedical subjects

A Viotti

Publications and source records attributed to A Viotti.

29 records · Page 2Linked to original sources

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↗

PubMed1983

Two adjacent genomic zein sequences: structure, organization and tissue-specific restriction pattern.

A clone isolated from a library of genomic clones from Zea mays contains two adjacent zein light-chain genes. The nucleotide sequence of the two coding regions and their flanking sequences shows that the two genes represent two different subclasses of light-chain zeins. One belongs to an abundant and highly conserved class and the other, which is 88% homologous to the first, is less represented in the genome of maize line W64A. Both genes present in clone zE are anomalous: one contains a mutation that introduces a termination codon after 39 amino acids, the other has the ATG initiation codon mutated to CTG. The presence of inversions, insertions and short inverted or direct repeats in the flanking sequences suggests that zein genes may be subject to rearrangements and transpositions. Southern blot analysis of genomic DNA indicates that the particular arrangement represented by clone zE is present at least four times in maize line W64A but other arrangements are found in this and other maize lines. DNA extracted from different tissues and developmental stages is digested differently by enzymes sensitive to methylation of their target sequence. The results indicate that zein genes contain methylated sites that are demethylated in correlation with their expression.

Base Sequence↗

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↗

PubMed1982

A homologous repetitive block structure underlies the heterogeneity of heavy and light chain zein genes.

Heavy and light chain zein genes from maize, affected by different regulatory loci, are related in sequence and structure. The two kinds of genes code for a signal peptide, a head region of 67 amino acids, six and a half to eight repetitive blocks of 20 amino acids each and a short tail piece. This block structure would allow inter or intragenic recombination giving rise to heterogeneous zein genes. Length variation in zein polypeptides is also due to the occurrence of termination mutations within some genes. Homology between heavy and light chain zein genes extends to the flanking sequences where a short region at the 5' end of the transcript can base pair with the 3' end and may have regulatory implications.

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↗

PubMed1978

Adaptation of the tRNA population of maize endosperm for zein synthesis.

Maize endosperm, 30 days after pollination is actively synthesizing zein, a storage protein containing high amounts of glutamine. leucine and alanine. Endosperm tRNAs have a higher accepting activity than embryo tRNAs for these three amino acids, but not for some other (control) amino acids. This increase in accepting activity is accompanied by a change in the distribution of the isoaccepting tRNA species corresponding to these three amino acids, but not of the isoacceptors corresponding to some other (control) amino acids. These results are in favor of the theory of functional adaptation of tRNA population.

Alanine↗

PubMed1975