RESUMO
This is the first study to investigate the molecular-genetic organization of polytene chromosome interbands located on both molecular and cytological maps of Drosophila genome. The majority of the studied interbands contained one gene with a single transcription initiation site; the remaining interbands contained one gene with several alternative promoters, two or more unidirectional genes, and "head-to-head" arranged genes. In addition, intricately arranged interbands containing three or more genes in both unidirectional and bidirectional orientation were found. Insulator proteins, ORC, P-insertions, DNase I hypersensitive sites, and other open chromatin structures were situated in the promoter region of the genes located in the interbands. This area is critical for the formation of the interband, an open chromatin region in which gene transcription and replication are combined.
Assuntos
Elementos de DNA Transponíveis , Genes Essenciais , Cromossomos Politênicos/genética , Regiões Promotoras Genéticas , Animais , Drosophila melanogasterRESUMO
The molecular and chromosomal localization of the dunce gene was studied. This gene (167.3 kb) consists almost entirely of introns, in which a cluster of seven short tissue-specific genes is located. On the basis of the results of FISH analysis of the gene fragments, we established that the dunce gene is located within nine chromosomal structures (four bands and five interbands), which contradicts the common idea that genes are located in only one structure (band or interband) or at the boundary of these structures. Our results are quite unexpected and original and greatly expand the current understanding of the genetic organization of interphase chromosomes.
Assuntos
Mapeamento Cromossômico , Proteínas de Drosophila/genética , Cromossomos Politênicos/genética , Animais , Drosophila melanogasterRESUMO
The precise genomic localization of the borders of 62 intercalary heterochromatin bands in Drosophila polytene chromosomes was determined. A new type of bands containing chromatin of different states was identified. This type is a combination of the gray band and the intercalary heterochromatin band, creating a genetic structure that with a light microscope is identified as a continuous band. The border structure of such bands includes the coding regions of genes with ubiquitous activity.
Assuntos
Drosophila melanogaster/genética , Heterocromatina/genética , Cromossomos Politênicos/genética , Animais , GenômicaRESUMO
New data on the organization of genes entirely located in the open domains for chromatin transcription and occupying only one chromosome structure (interband) were obtained. The characteristic features of these genes are the small size (on average, 1-2 kb), depletion of the replicative complex proteins in the regulatory region, and the presence of specific motifs for binding transcription factors, as compared to the genes occupying two structures (interband and gray band). The biological function of these genes is associated primarily with the processes of gene expression and RNA metabolism.
Assuntos
Cromatina , Proteínas de Ligação a DNA , Proteínas de Drosophila , Regulação da Expressão Gênica/fisiologia , Cromossomos Politênicos , RNA , Animais , Cromatina/genética , Cromatina/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster , Cromossomos Politênicos/genética , Cromossomos Politênicos/metabolismo , RNA/biossíntese , RNA/genéticaRESUMO
Genetic organization of bands and interbands in polytene chromosomes has long remained a puzzle for geneticists. It has been recently demonstrated that interbands typically correspond to the 5'-ends of house-keeping genes, whereas adjacent loose bands tend to be composed of coding sequences of the genes. In the present work, we made one important step further and mapped two large introns of ubiquitously active genes on the polytene chromosome map. We show that alternative promoter regions of these genes map to interbands, whereas introns and coding sequences found between those promoters correspond to loose grey bands. Thus, a gene having its long intron "sandwiched" between to alternative promoters and a common coding sequence may occupy two interbands and one band in the context of polytene chromosomes. Loose, partially decompacted bands appear to host large introns.
Assuntos
Drosophila/genética , Íntrons , Cromossomos Politênicos/genética , Animais , Genes de Insetos , Mapeamento Físico do CromossomoRESUMO
Genetic activity of interphase chromosomes is associated with their structural organization, but the mechanism of these relations is still unclear. Classic polythene chromosomes of dipteran insects are a convenient model for such investigations. Despite intensive study of polythene chromosomes of Drosophila melanogaster is carried out, an exact conformity of bands and interbands to the molecular map of the genome remains unknown in most cases. For addressing this issue, the genetic map and molecular characteristics of chromatin have been compared with the banding pattern of the fourth chromosome, which is the smallest chromosome in the D. melanogaster genome and is different in many ways from other chromosomes. This is a unique chromatin domain of D. melanogaster, which is characterized by specific proteins, including HP1, POF and EGG. Matching of cytological and physical maps of the fourth chromosome has been carried out by FISH. Genomic coordinates of bands and interbands have been determined. This result makes it possible to investigate the regulation of gene activity of the fourth chromosome in the context of molecular characteristics of cytological structures in which these genes are located.
Assuntos
Mapeamento Cromossômico/métodos , Proteínas de Drosophila/genética , Cromossomos Politênicos/genética , Animais , Drosophila melanogasterRESUMO
Classic polythene chromosomes from dipteran insects are extensively used as a model for interphase chromosomes. The peculiar morphology of polythene chromosomes is formed by the alternating densely packed chromatin of bands and less compact interbands. In recent years numerous data have been obtained on the precise localization of different proteins on the molecular map in the interphase chromosomes. A special algorithm has been developed based on the interband specific protein composition. This algorithm allows us to detect the positions of bands and interbands in the whole Drosophila's genome. The goal of our investigation is to analyse of P-elements distribution in localized bands and interbands. We have found that P-elements distribution is not random in Drosophila's genome. Insertions of P-elements predominantly take place in regions of genome predicted by algorithm as interbands. The density of P-element insertions in compacted bands is notably lower.
