Polytene chromosomes normal.
Nucleotide substitution: G 121 to CT, resulting in a frameshift of the protein beginning at amino acid residue 41.
G13965128T
G?CT
A41S | Orc2-PA
Substitution of a CT for a G causes a frameshift at amino acid 41.
mitosis & nuclear chromosome
mitosis & nuclear chromosome (with Orc21)
Orc2γ4 somatic clones contain fewer cells compared with their wild-type twin clones. Although proliferation is perturbed, the cell size, the nuclear size, and DNA content of the twin clones are indistinguishable between homologous and wild-type clones.
Orc2γ4 follicle cell clones contain two to three cells, always fewer than their sister clones, consistent with the idea that Orc1 is required for proliferation.
Examination of mutant larval neuroblasts reveals many severe mitotic defects. More than 90% of mitotic figures are abnormal. Most frequently, mitotic chromosomes contain regions of undercondensed chromatin connected by normally condensed chromatin connected by normally condensed or even highly condensed chromatin, the same undercondensed region often visibly affected on both sister chromatids. No normal anaphase figures are seen and their frequency is greatly reduced compared to wild-type. Chromosome breaks and rearrangements are also seen - including single and double sister chromatid breaks complex rearrangements, small supernumerary chromosomes containing sequences derived from chromosome X 2 or 3, however heterochromatic sequences are only very rarely undercondensed in these chromosomes. Mutant salivary glands are of normal size and polytene chromosomes appear to have normal banding and polyploidisation. After 24 hours of BrdU feeding a 13-22 fold decrease in the percentage of mutant cells that have entered S phase is seen. There is also a significant increase in the number of cells seen to be in G1 phase. In mutants the metaphase to anaphase ratio is 13-21 fold higher than in wild-type cells. The temporal control of replication is altered in mutant larvae. Unlike wild-type (where late replication is confined solely to centromeric heterochromatic) some areas of euchromatin are seen to replicate very late, even after heterochromatic domains. The late replicating areas of euchromatin exhibit the greatest problems in mitotic condensation.
Shows no dominant effect on telomeric Position Effect Variegation (PEV) in stocks carrying a variegating w+mW.hs allele at the telomeres of the second and third chromosomes.
Homozygous larvae show poor polytenisation of chromosomes.
Expression of Orc2T:Avic\GFP.N rescues the lethality seen in Orc22/Orc2γ4.
Expression of Orc2T:Avic\GFP.C rescues the lethality seen in Orc22/Orc2γ4.
Adult flies expressing Orc2T:Avic\GFP.N in a Orc22/Orc2γ4 background eclose at day 11 after egg deposition compared to 10 days in wild type.
Adult flies expressing Orc2T:Avic\GFP.C in a Orc22/Orc2γ4 background eclose at day 11 after egg deposition compared to 10 days in wild type.
