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Andre R O Cavalcanti

Publications and source records attributed to Andre R O Cavalcanti.

15 recordsLinked to original sources
PubMed2006

Interconversion of germline-limited and somatic DNA in a scrambled gene.

Ciliates have a somatic and a germline nucleus; after sexual conjugation a new somatic nucleus forms from the new zygotic germline nucleus. Formation of the somatic nucleus involves precise elimination of a large portion of DNA sequences from the germline. Here we compare the architecture of the germline and somatic versions of the actin I gene in two geographically isolated strains of Stylonychia lemnae. We show that the structure of the germline gene is surprisingly mercurial, with the distinction between germline-limited and somatic sequences variable over the course of evolution. This is, to our knowledge, the first example of evolutionary swapping of retained versus deleted sequences during ciliate development, with sequences deleted during development that are specifically retained in another strain.

Actins↗
PubMed2006

On the paucity of duplicated genes in Caenorhabditis elegans operons.

Spliced leader trans-splicing is an mRNA maturation process used by a small set of eukaryotes, including the nematode C. elegans, to cap the downstream genes of operons. We analyzed the frequency of duplication of operonic genes in C. elegans and confirmed that they are duplicated less often in the genome than monocistronic genes. Because operons account for about 15% of the genes in C. elegans, this lower duplication frequency might place a large constraint on the plasticity of the genome. Further analyses suggest that this paucity of duplicated genes results from operon organization hindering specific types of gene duplication.

Animals↗
PubMed2005

Conservation of tandem stop codons in yeasts.

BACKGROUND: It has been long thought that the stop codon in a gene is followed by another stop codon that acts as a backup if the real one is read through by a near-cognate tRNA. The existence of such 'tandem stop codons', however, remains elusive. RESULTS: Here we show that a statistical excess of stop codons has evolved at the third codon downstream of the real stop codon UAA in yeasts. Comparative analysis indicates that stop codons at this location are considerably more conserved than sense codons, suggesting that these tandem stop codons are maintained by selection. We evaluated the influence of expression levels of genes and other biological factors on the distribution of tandem stop codons. Our results suggest that expression level is an important factor influencing the presence of tandem stop codons. CONCLUSIONS: Our study demonstrates the existence of tandem stop codons, which represent one of many meaningful genomic features that are driven by relatively weak selective forces.

Base Sequence↗
PubMed2005

MDS_IES_DB: a database of macronuclear and micronuclear genes in spirotrichous ciliates.

Ciliated protozoa have two kinds of nuclei: Macronuclei (MAC) and Micronuclei (MIC). In some ciliate classes, such as spirotrichs, most genes undergo several layers of DNA rearrangement during macronuclear development. Because of such processes, these organisms provide ideal systems for studying mechanisms of recombination and gene rearrangement. Here, we describe a database that contains all spirotrich genes for which both MAC and MIC versions are sequenced, with consistent annotation and easy access to all the features. An interface to query the database is available at http://oxytricha.princeton.edu/dimorphism/database.htm.

Animals↗
PubMed2005

Decoding the decoding region: analysis of eukaryotic release factor (eRF1) stop codon-binding residues.

Peptide synthesis in eukaryotes terminates when eukaryotic release factor 1 (eRF1) binds to an mRNA stop codon and occupies the ribosomal A site. Domain 1 of the eRF1 protein has been implicated in stop codon recognition in a number of experimental studies. In order to further pinpoint the residues of this protein involved in stop codon recognition, we sequenced and compared eRF1 genes from a variety of ciliated protozoan species. We then performed a series of computational analyses to evaluate the conservation, accessibility, and structural environment of each amino acid located in domain 1. With this new dataset and methodology, we were able to identify eight specific amino acid sites important for stop codon recognition and also to propose a set of cooperative paired substitutions that may underlie stop codon reassignment. Our results are more consistent with current experimental data than previously described models.

Amino Acid Sequence↗
PubMed2004

Coding properties of Oxytricha trifallax (Sterkiella histriomuscorum) macronuclear chromosomes: analysis of a pilot genome project.

The macronuclear genomes of spirotrichous ciliates are almost entirely polyploid, single-gene chromosomes ("nanochromosomes"). We recently performed a pilot genome project for a member of this group, Oxytricha trifallax ( Sterkiella histriomuscorum), in which approximately 2000 nanochromosomes were cloned at random and end-sequenced. Here we describe the global properties of the coding regions predicted for these molecules, including nucleotide composition, codon usage, and intron properties. In identifying splice donor, acceptor and branch sites, we found that longer introns in Oxytricha have a stronger signal at the donor site than do smaller introns, as has been found for Caenorhabditis elegans and Drosophila, despite the overall small size of the introns. A systematic search for multi-gene chromosomes identified 11 candidate nanochromosomes. We compare the results from this large dataset with those obtained from earlier studies and with statistics recorded from ciliates and other eukaryotes.

Animals↗
PubMed2004

Genetic code.

Explore the source record for details and available documents.

Amino Acids↗
PubMed2004

Gene Unscrambler for detangling scrambled genes in ciliates.

UNLABELLED: Scrambled genes are surprisingly common in some species of ciliates. Until now there was no software available to analyze automatically these genes. We present here a program that can automatically align the macronuclear and micronuclear forms of a gene, outputting the location of the macronuclear destined segments and pointer sequences. AVAILABILITY: A web version of the program is available free of charge and can be accessed at http://oxytricha.princeton.edu/GeneUnscrambler.htm

Algorithms↗
PubMed2004

On the classes of aminoacyl-tRNA synthetases, amino acids and the genetic code.

The division of the aminoacyl-tRNA synthetases in two classes is compared with a division of the amino acids in two classes, obtained from the AAIndex databank by a principal component analysis. The division of the enzymes in Classes I and II follows to a great extent a division in the chemical and biological properties of their cognate amino acids. Furthermore, the phylogenetic trees of Classes I and II enzymes are highly correlated with dendrograms obtained for their cognate amino acids by using the indices in the AAIndex database. We argue that the evolution of aminoacyl-tRNA synthetases was determined by the characteristics of their corresponding amino acids. We interpret these results considering models for the origin and evolution of the genetic code in which an initial version, containing fewer amino acids, was modified by the incorporation of new amino acids following duplication and divergence of previous synthetases and tRNA molecules.

Amino Acids↗
PubMed2004

Sequence features of Oxytricha trifallax (class Spirotrichea) macronuclear telomeric and subtelomeric sequences.

We sequenced and analyzed the subtelomeric regions of 1356 macronuclear "nanochromosomes" of the spirotrichous ciliate Oxytricha trifallax. We show that the telomeres in this species have a length of 20 nt, with minor deviations; there is no correlation between telomere lengths at the two ends of the molecule. A search for open reading frames revealed that the 3' and 5' untranslated regions are short, with a median length of approximately 130 nt, and that surprisingly there are no detectable differences between sequences upstream and downstream of genes. Our results confirm a previously reported purine bias in the first approximately 80 nucleotides of the subtelomeric regions, but with this larger data set we curiously detected a 10 bp periodicity in the bias; we relate this finding to the possible regulatory and structural functions these regions must serve. Palindromic sequences in opposing subtelomeric regions, although present in most sequences, are not statistically significant.

Animals↗
PubMed2003

Patterns of gene duplication in Saccharomyces cerevisiae and Caenorhabditis elegans.

In this paper we present a new method for detecting block duplications in a genome. It is more stringent than previous ones in that it requires a more rigorous definition of paralogous genes and that it requires the paralogous proteins on the two blocks to be contiguous. In addition, it provides three criterion choices: (1) the same composition (i.e., having the same paralogues in the two windows), (2) the same composition and gene order, and (3) the same composition, gene order, and gene orientation. The method is completely automated, requiring no visual inspection as in previous methods. We applied it to analyze the complete genomes of S. cerevisiae and C. elegans. In yeast we detected fewer duplicated blocks than previously reported. In C. elegans, however, we detected more block duplications than previously reported, indicating that although our method has a more stringent definition of block duplication than previous ones, it may be more sensitive in detection because it considers every possible window rather than only fixed nonoverlapping windows. Our results show that block duplication is a common phenomenon in both organisms. The patterns of block duplication in the two species are, however, markedly different. The yeast shows much more extensive block duplication than the nematode, with some chromosomes having more than 40% of the duplications derived from block duplications. Moreover, in the yeast the majority of block duplications occurred between chromosomes, while in the nematode most block duplications occurred within chromosomes.

Animals↗
PubMed2003

Detection of gene duplications and block duplications in eukaryotic genomes.

Several eukaryotic genomes have been completely sequenced and this provides an opportunity to investigate the extent and characteristics (e.g., single gene duplication, block duplication, etc.) of gene duplication in a genome. Detecting duplicate genes in a genome, however, is not a simple problem because of several complications such as domain shuffling, the existence of isoforms derived from alternative splicing, and annotational errors in the databases. We describe a method for overcoming these difficulties and the extents of gene duplication in the genomes of Drosophila melanogaster, Caenorhabditis elegans, and yeast inferred from this method. We also describe a method for detecting block duplications in a genome. Application of this method showed that block duplication is a common phenomenon in both yeast and nematode. The patterns of block duplication in the two species are, however, markedly different. Yeast shows much more extensive block duplication than nematode, with some chromosomes having more than 40% of the duplications derived from block duplications. Moreover, in yeast the majority of block duplications occurred between chromosomes, while in nematode most block duplications occurred within chromosomes.

Animals↗