Biomedical subjects

L M Montero

Publications and source records attributed to L M Montero.

5 recordsLinked to original sources

PubMed1993

Non-random distribution of transposable elements in the nuclear genome of plants.

We have studied the genomic distribution of five different families of plant transposable elements by analyzing their location in DNA fractions from maize and tobacco genomes fractionated according to base composition. The results show that each family of elements is preferentially integrated in one specific fraction of its respective host genome. This demonstrates that the distribution of transposable elements in the nuclear genome of plants is not random but compartmentalized, i.e., the elements are located in specific genomic compartments characterized by having a specific G+C content and representing a small proportion of the genomes. Furthermore, these compartments seem to correspond to the genomic regions where most of the plant genes are also located, suggesting a preferential integration of transposable elements in the transcriptionally active regions of the plant genome. The implications of these results on the current applications of transposon tagging techniques are discussed.

Base Composition↗

PubMed1992

The distribution of 5-methylcytosine in the nuclear genome of plants.

We have determined the 5-methylcytosine (5mC) content in high molecular weight DNA, from two dicot (tobacco and pea) and two monocot (wheat and maize) plant species, fractionated according to base composition. The results show that the proportion of 5mC in the genomic fractions increases linearly with their guanine + cytosine (G + C) content while the proportion of non-methylated cytosine remains almost constant. This can be interpreted as a consequence of a difference in mutation pressure related to spontaneous deamination of 5mC to thymine between the different compartments of plant genomes.

5-Methylcytosine↗

PubMed1990

Gene distribution and isochore organization in the nuclear genome of plants.

The genomic distribution of 23 nuclear genes from three dicotyledons (pea, sunflower, tobacco) and five monocotyledons of the Gramineae family (barley, maize, rice, oat, wheat) was studied by localizing these genes in DNA fractions obtained by preparative centrifugation in Cs2SO4/BAMD density gradients. Each one of these genes (and of many other related genes and pseudogenes) was found to be located in DNA fragments (50-100 Kb in size) that were less than 1-2% GC apart from each other. This definitively demonstrates the existence of isochores in plant genomes, namely of compositionally homogeneous DNA regions at least 100-200 Kb in size. Moreover, the GC levels of the 23 coding sequences studied, of their first, second and third codon positions, and of the corresponding introns were found to be linearly correlated with the GC levels of the isochores harboring those genes. Compositional correlations displayed increasing slopes when going from second to first to third codon position with obvious effects on codon usage. Coding sequences for seed storage proteins and phytochrome of Gramineae deviate from the compositional correlations just described. Finally, CpG doublets of coding sequences were characterized by a shortage that decreased and vanished with increasing GC levels of the sequences. A number of these findings bear a striking similarity with results previously obtained for vertebrate genes.

Animals↗

PubMed1989

The isochore organization and the compositional distribution of homologous coding sequences in the nuclear genome of plants.

The isochore structure of the nuclear genome of angiosperms described by Salinas et al. (1) was confirmed by using a different experimental approach, namely by showing that the levels of coding sequences from both dicots and Gramineae are linearly correlated with GC levels of the corresponding flanking sequences. The compositional distribution of homologous coding sequences from several orders of dicots and from Gramineae were also studied and shown to mimick the compositional distributions previously seen (1) for coding sequences in general, most coding sequences from Gramineae being much higher than those of the dicots explored. These differences were even stronger for third codon positions and led to striking codon usages for many coding sequences especially in the case of Gramineae.

Cell Nucleus↗

PubMed1988

Compositional compartmentalization and compositional patterns in the nuclear genomes of plants.

We report here results which indicate (i) that the nuclear genomes of angiosperms is characterized by a compositional compartmentalization and an isochore structure; and (ii) that the nuclear genomes of some Gramineae exhibit strikingly different compositional patterns compared to those of many dicots. Indeed, the compositional distribution of nuclear DNA molecules (in the 50-100 Kb size range) from three dicots (pea, sunflower and tobacco) and three monocots (maize, rice and wheat) were found to be centered around lower (41%) and higher (45% for rice, 48% for maize and wheat) GC levels, respectively (and to trail towards even higher GC values in maize and wheat). Experiments on gene localization in density gradient fractions showed a remarkable compositional homogeneity in vast (greater than 100-200 Kb) regions surrounding the genes. On the other hand, the compositional distribution of coding sequences (GenBank and literature data) from dicots (several orders) was found to be narrow, symmetrical and centered around 46% GC, that from monocots (essentially barley, maize and wheat) to be broad, asymmetrical and characterized by an upward trend towards high GC values, with the majority of sequences between 60 and 70% GC. Introns exhibited a similar compositional distribution, but lower GC levels, compared to exons from the same genes.

Cell Nucleus↗