Statistical evaluation of the coding capacity of complementary DNA strands

Identification and chromosomal localization of one locus of Leishmania (L.) major related with resistance to itraconazole

Ergosterol is an important compound responsible to maintain integrity and fluidity of Leishmania spp. membranes. Starting from an overexpression/selection method, our group has isolated and mapped nine different loci of Leishmania (L.) major related to resistance against two inhibitors of the ergosterol biosynthesis pathway, terbinafine (TBF) and itraconazole (ITZ). Individual functional analysis after overexpression induction of these loci in the presence of TBF and/or ITZ [or the ITZ analog ketoconazole (CTZ)] have shown low but significant levels of resistance after transfection into L. major wild-type parasites. In this work, we have shown the insert mapping and chromosomal identification of one of these loci (cosItz2). Functional analysis experiments associated with chromosomal localization by comparison at genomic database allowed us to identify two prospective gene-protein systems not related to the ergosterol biosynthesis and capable to confer wild-type cells resistance to ITZ-CTZ after transfection. We expected that this approach can open new insights for a better understanding of mechanisms of ITZ-CTZ action and resistance in Leishmania resulting in new strategies for the leishmaniasis treatment.

Organization of H locus conserved repeats in Leishmania (Viannia) braziliensis correlates with lack of gene amplification and drug resistance

Resistance to antimonials is a major problem when treating visceral leishmaniasis in India and has already been described for New World parasites. Clinical response to meglumine antimoniate in patients infected with parasites of the Viannia sub-genus can be widely variable, suggesting the presence of mechanisms of drug resistance. In this work, we have compared L. major and L. braziliensis mutants selected in different drugs. The cross-resistance profiles of some cell lines resembled those of mutants bearing H locus amplicons. However, amplified episomal molecules were exclusively detected in L. major mutants. The analysis of the L. braziliensis H region revealed a strong conservation of gene synteny. The typical intergenic repeats that are believed to mediate the amplification of the H locus in species of the Leishmania sub-genus are partially conserved in the Viannia species. The conservation of these non-coding elements in equivalent positions in both species is indicative of their relevance within this locus. The absence of amplicons in L. braziliensis suggests that this species may not favour extra-chromosomal gene amplification as a source of phenotypic heterogeneity and fitness maintenance in changing environments.

Antisense overlapping open reading frames in genes from bacteria to humans

Long Open Reading Frames (ORFs) in antisense DNA strands have been reported in the literature as being rare events. However, an extensive analysis of the GenBank database revealed that a substantial number of genes from several species contain an in-phase ORF in the antisense strand, that overlaps entirely the coding sequence of the sense strand, or even extends beyond. The findings described in this paper show that this is a frequent, non-random phenomenon, which is primarily dependent on codon usage, and to a lesser extent on gene size and GC content. Examination of the sequence database for several prokaryotic and eukaryotic organisms, demonstrates that coding sequences with in-phase, 100% overlapping antisense ORFs are present in every genome studied so far.

Trans-splicing of pre-mRNA is predicted to occur in a wide range of organisms including vertebrates

Several known trans-splicing RNA structures were used to define a canonical trans-splicing structure which was then used to perform a computer search of the EMBL nucleotide database. In addition to most known trans-splicing structures, many putative new trans-splicing sites were detected. These were found in a broad range of organisms including the vertebrates. Control experiments indicate that the search predicts known false positives at a rate of only 20%. Trans-splicing may therefore be a very wide-spread phenomenon.

Tight linkage of glnA and a putative regulatory gene in Rhizobium leguminosarum

Rhizobium leguminosarum, biovar viceae, strain RCC1001 contains two glutamine synthetase activities, GSI and GSII. We report here the identification of glnA, the structural gene for GSI. A 2 kb fragment of DNA was shown to complement the Gln- phenotype of Klebsiella pneumoniae glnA mutant strains. DNA sequence analysis revealed an open reading frame (ORF) of 469 codons specifying a polypeptide of 52,040 daltons. Its deduced amino acid sequence was found to be highly homologous to other glutamine synthetase sequences. This ORF was expressed in Escherichia coli minicells and the corresponding polypeptide reacted with an antiserum raised against GSI. Upstream of glnA we found an ORF of 111 codons (ORF111) preceded by the consensus sequence for an ntrA-dependent promoter. Minicells experiments showed a protein band, with a molecular weight in good agreement with that (10,469) deduced from the nucleotide sequence. On the basis of homology studies we discuss the possibility that the product of ORF111 is equivalent to the PII protein of E. coli and plays a similar role in regulation of nitrogen metabolism.

Structure of the highly repeated, long interspersed DNA family (LINE or L1Rn) of the rat

We present the DNA sequence of a 6.7-kilobase member of the rat long interspersed repeated DNA family (LINE or L1Rn). This member (LINE 3) is flanked by a perfect 14-base-pair (bp) direct repeat and is a full-length, or close-to-full-length, member of this family. LINE 3 contains an approximately 100-bp A-rich right end, a number of long (greater than 400-bp) open reading frames, and a ca. 200-bp G + C-rich (ca. 60%) cluster near each terminus. Comparison of the LINE 3 sequence with the sequence of about one-half of another member, which we also present, as well as restriction enzyme analysis of the genomic copies of this family, indicates that in length and overall structure LINE 3 is quite typical of the 40,000 or so other genomic members of this family which would account for as much as 10% of the rat genome. Therefore, the rat LINE family is relatively homogeneous, which contrasts with the heterogeneous LINE families in primates and mice. Transcripts corresponding to the entire LINE sequence are abundant in the nuclear RNA of rat liver. The characteristics of the rat LINE family are discussed with respect to the possible function and evolution of this family of DNA sequences.

New statistical approach to discriminate between protein coding and non-coding regions in DNA sequences and its evaluation

We propose a new approach to study protein coding and non-coding regions in DNA sequences, by making use of two complementary statistical methods. The principal component analysis (PCA) is a graphical method to represent DNA sequences which are characterized by some quantitative parameters: it is a help to the intuition. The discriminating analysis (DA) is a quantitative method which permits to classify the DNA sequences. It leads to an evaluation of the first method and to a decision. The value of this approach has been confirmed since we also have found some results which had been described recently in the literature. Furthermore, this general methodology has permitted us to show the existence of parameters which identify the nucleic acid sequence functional domains, without having to make use of the properties of the genetic code.

Structure of the highly repeated, long interspersed DNA family (LINE or L1Rn) of the rat

We present the DNA sequence of a 6.7-kilobase member of the rat long interspersed repeated DNA family (LINE or L1Rn). This member (LINE 3) is flanked by a perfect 14-base-pair (bp) direct repeat and is a full-length, or close-to-full-length, member of this family. LINE 3 contains an approximately 100-bp A-rich right end, a number of long (greater than 400-bp) open reading frames, and a ca. 200-bp G + C-rich (ca. 60%) cluster near each terminus. Comparison of the LINE 3 sequence with the sequence of about one-half of another member, which we also present, as well as restriction enzyme analysis of the genomic copies of this family, indicates that in length and overall structure LINE 3 is quite typical of the 40,000 or so other genomic members of this family which would account for as much as 10% of the rat genome. Therefore, the rat LINE family is relatively homogeneous, which contrasts with the heterogeneous LINE families in primates and mice. Transcripts corresponding to the entire LINE sequence are abundant in the nuclear RNA of rat liver. The characteristics of the rat LINE family are discussed with respect to the possible function and evolution of this family of DNA sequences.

Probability of coding of a DNA sequence: an algorithm to predict translated reading frames from their thermodynamic characteristics

An algorithm to determine the probability that a reading frame codifies for a protein is presented. It is based on the results of our previous studies on the thermodynamic characteristics of a translated reading frame. We also develop a prediction procedure to distinguish between coding and non-coding reading frames. The procedure is based on the characteristics of the putative product of the DNA sequence and not on periodicity characteristics of the sequence, so the prediction is not biased by the presence of overlapping translated reading frames or by the presence of translated reading frames on the complementary DNA strand.