ABSTRACT
AIMS: To study the transcriptional analysis of glutamate dehydrogenase gene, involved in the amino acid conversion to aroma compound in Streptococcus thermophilus. METHODS AND RESULTS: Analysis of the gdhA gene nucleotide sequence of S. thermophilus CNRZ1066 revealed that the coding region is 1353 nucleotides long. The deduced amino acids sequence exhibits the putative GDH active site and some conserved domains characteristic of family I of hexameric GDHs. Phylogenetic analysis revealed that the gdh gene of S. thermophilus clustered with the orthologues of other streptococci such as Streptococcus mutans, Streptococcus agalactiae and Streptococcus infantarius. Studying the structural organization of the gdhA locus the amino acid similarity of GDHs was higher than 87%, but the locus organization was not conserved. A dominant transcript of approximately 1.4 kbp was revealed by Northern blot hybridization, suggesting that gdhA mRNA is monocystronic. Primer extension showed that transcription start point of gdhA was localized 43 bp upstream of the potential start codon (ATG). CONCLUSIONS: The gdhA represents a monocistronic operon highly conserved in phylogenetic-related bacteria. SIGNIFICANCE AND IMPACT OF THE STUDY: A deeper knowledge of gdh transcriptional mechanisms could lead to develop S. thermophilus industrial starter cultures with optimized aromatic properties.
Subject(s)
Glutamate Dehydrogenase/genetics , Streptococcus thermophilus/genetics , Transcription, Genetic/genetics , Amino Acid Sequence , Bacterial Proteins/genetics , Base Sequence , Blotting, Northern , DNA Primers/genetics , DNA, Bacterial/genetics , Molecular Sequence Data , Phylogeny , RNA, Bacterial/genetics , RNA, Messenger/genetics , Sequence Analysis, DNAABSTRACT
Foldback ( FB) elements are transposable elements found in many eukaryotic genomes; they are thought to contribute significantly to genome plasticity. In Drosophila melanogaster, FBs have been shown to be involved in the transposition of large chromosomal regions and in the genetic instability of some alleles of the white gene. In this report we show that FB mediated transposition of w(67C23), a mutation that deletes the promoter of the white gene and its first exon, containing the start codon, can restore expression of the white gene. We have characterized three independent events in which a 14-kb fragment from the w(67C23) locus was transposed into an intron region in three different genes. In each case a local promoter drives the expression of white, producing a chimeric mRNA. These findings suggest that, on an evolutionary timescale, FB elements may contribute to the creation of new genes via exon shuffling.
Subject(s)
ATP-Binding Cassette Transporters/genetics , DNA Transposable Elements , Drosophila Proteins/genetics , Drosophila melanogaster/genetics , Exons/genetics , Eye Proteins/genetics , Mutation , Promoter Regions, Genetic , Selection, Genetic , ATP-Binding Cassette Transporters/metabolism , Alleles , Animals , Drosophila Proteins/metabolism , Eye Proteins/metabolism , Gene Deletion , IntronsABSTRACT
A homogeneous array of 80 tandem repeats of the Bari1 transposon is located in the pericentromeric h39 region of chromosome 2 of Drosophila melanogaster. Here, we report that the Bari1 cluster is interrupted by an 8556-bp insertion. DNA sequencing and database searches identified this insertion as a previously unannotated retrotransposon that we have named MAX. MAX possesses two ORFs; ORF1 putatively encodes a polyprotein comprising GAG and RT domains, while ORF2 could encode a 288-amino acid protein of unknown function. Alignment with the RT domains of known LTR retrotransposons shows that MAX belongs to the BEL-Pao family, which remarkable for its widespread presence in different taxa, including lower chordates. We have analyzed the distribution of MAX elements within representative species of the Sophophora subgroup and found that they are restricted to the species of the melanogaster complex, where they are heavily represented in the heterochromatin of all autosomes and on the Y chromosome.
Subject(s)
Chromosome Mapping , DNA-Binding Proteins/genetics , Drosophila Proteins/genetics , Drosophila melanogaster/genetics , Heterochromatin/genetics , Retroelements/genetics , Transcription Factors/genetics , Amino Acid Sequence , Animals , Basic Helix-Loop-Helix Leucine Zipper Transcription Factors , Drosophila/genetics , Male , Molecular Sequence Data , Multigene Family , Oligonucleotide Array Sequence Analysis , Phylogeny , Sequence Alignment , Sequence Homology, Amino Acid , Y Chromosome/geneticsABSTRACT
We have determined the structure and organization of Tirant, a retrotransposon of Drosophila melanogaster reported in literature to be responsible for four independent mutations. Tirant is a long terminal repeat (LTR) retrotransposon 8527bp long. It possesses three open reading frames (ORF) encoding Gag, Pol and Env proteins with a strong similarity with ZAM, a recently identified member of the gypsy class of retrovirus-like mobile elements. Molecular analysis of the Tirant genomic copies present in four D. melanogaster strains revealed that most of them are defective, non-autonomous elements that differ in the position and extension of the conserved internal portion. Defective elements lacking the Gag ORF but retaining the Env ORF are abundant in heterochromatin. Four discrete Tirant transcripts are observed during embryogenesis in the strain Oregon-R, the smaller of which, 1.8kb in size, originates from the splicing of a primary transcript and leads to a subgenomic RNA coding for the Env product.
