RESUMO
Mobile genetic elements affect structure and function in various ways. Significant number of genes in human and mouse are transcribed from alternative promoters located in LTR retrotransposons. As a rule, these retrotransposons are located upstream of annotated genes, and their promoters initiate transcription of alternative first exon. We investigated role of LTR retrotransposons in expression of genes in Drosophila. Using database of spliced ESTs we identified only 13 potential cases of transcription initiation from long terminal repeats of LTR within euchromatic part of the Drosophila genome. Our results indicate on insignificant role of promoters of LTR retrotransposons in expression of genes in Drosophila.
Assuntos
Drosophila melanogaster/genética , Genoma de Inseto , Retroelementos , Animais , Bases de Dados de Ácidos Nucleicos , Etiquetas de Sequências Expressas , Genes de Insetos , Regiões Promotoras Genéticas , Transcrição GênicaRESUMO
Different genome regions differ in replication timing during the S phase. Late-replicating sequences are often underreplicated in the Drosophila salivary-gland polytene chromosomes. The SuUR gene, whose mutation changes the replication time of late-replicating regions in salivary-gland cells, has been identified in Drosophila melanogaster. The SUUR protein lacks homologs by a BLAST search, and only moderate homology is observed between its N-terminal end and chromatin-remodeling proteins of the SWI2/SNF2 family. The gene and the protein were analyzed in insects. Orthologs of the SuUR gene were found in all annotated Drosophila species. The number of amino acid substitutions in the SUUR protein proved to be extremely high, corresponding to that of rapidly evolving genes. Orthologs with low homology were found in mosquitoes Anopheles gambiae, Aedes aegypti, and Culex quinquefasciatus. No orthologs of the SuUR gene were detected beyond Diptera.
Assuntos
Proteínas de Ligação a DNA/genética , Proteínas de Drosophila/genética , Proteínas de Insetos/genética , Aedes/genética , Sequência de Aminoácidos , Animais , Anopheles/genética , Culex/genética , Drosophila/genética , Dados de Sequência Molecular , Filogenia , Homologia de Sequência de AminoácidosRESUMO
A significant portion of a eukaryotic genome is silent (epigenetically repressed). In Drosophila melanogaster, this portion includes mainly regions of pericentric and intercalary heterochromatin and euchromatin regions subject to position-effect variegation. Detailed study of the organization of intercalary heterochromatin regions of Drosophila melanogaster polytene chromosomes started from the discovery of the SuUR gene (Suppressor of UnderReplication). The ability of the SuUR mutation to suppress underreplication in intercalary heterochromatin regions was used for molecular tagging of these regions. We showed that underreplicated intercalary heterochromatin regions contained silent unique genes and retained the features of late replication and transcriptionally inactive chromatin state in various cell types. Over 50% of these regions contain unique genes clustered on the base of coordinated expression. The origin of clusters and putative mechanisms of their gene expression are discussed. Data on the SuUR gene, its expression, and effect on polytene chromosome structure and replication are summarized.
