The bithorax complex of Drosophila melanogaster: Underreplication and morphology in polytene chromosomes.
The level of polyteny of the Drosophila salivary gland chromosomes was determined throughout the chromosome region 89E1-4, the locus of the Bithorax Complex. A zone of underreplication spans the 300 kb of DNA from the Ubx to Abd-B loci. From the centromere proximal end of the complex, a 70-kb-long gradual decrease of polytenization starts with the Ubx transcription unit and, after a floor corresponding to the abd-A locus, raises gradually back to the maximum over 70 kb in the region of the Abd-B transcription unit. In flies carrying the mutation Suppressor of DNA Underreplication [Su(UR)ES], the underreplication of the Bithorax Complex is fully suppressed. In the wild type, the Bithorax Complex forms a weak point featuring thinner bands separated by clefts or constrictions. In Su(UR)ES strain in contrast, the 89E1-4 band looks like a single solid band consisting of homogenous dense material. We speculate that the wild-type Su(UR)ES protein hampers DNA replication of silenced domains and leads to their underreplication in salivary gland polytene chromosomes.
Moshkin
Y M
YM
Institute of Cytology and Genetics, Siberian Division of Russian Academy of Sciences, Novosibirsk 630090, Russia.
Alekseyenko
A A
AA
Semeshin
V F
VF
Spierer
A
A
Spierer
P
P
Makarevich
G F
GF
Belyaeva
E S
ES
Zhimulev
I F
IF
D000818:Animals; D002875:Chromosomes / Q000235:genetics / Q000648:ultrastructure*; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics* / Q000254:growth & development / Q000648:ultrastructure; D005786:Gene Expression Regulation; D020868:Gene Silencing; D005801:Genes, Homeobox; D017344:Genes, Insect; D016153:Genes, Suppressor; D006570:Heterochromatin / Q000235:genetics / Q000648:ultrastructure*; D018398:Homeodomain Proteins / Q000235:genetics; D019476:Insect Proteins / Q000235:genetics / Q000502:physiology; D007814:Larva; D008854:Microscopy, Electron; D009687:Nuclear Proteins; D012469:Salivary Glands / Q000648:ultrastructure; D014157:Transcription Factors
D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D006570:Heterochromatin; D018398:Homeodomain Proteins; D019476:Insect Proteins; D009687:Nuclear Proteins; C464850:SuUR protein, Drosophila; D014157:Transcription Factors; C066177:Ubx protein, Drosophila; C066591:abd-A protein, Drosophila