The size and internal structure of a heterochromatic block determine its ability to induce position effect variegation in Drosophila melanogaster.
In the In(1LR)pn2a rearrangement, the 1A-2E euchromatic segment is transposed to the vicinity of X heterochromatin (Xh), resulting in position effect variegation (PEV) of the genes in the 2BE region. Practically the whole X-linked heterochromatin is situated adjacent to variegated euchromatic genes. Secondary rearrangements showing weakening or reversion of PEV were obtained by irradiation of the In(1LR)pn2a. These rearrangements demonstrate a positive correlation between the strength of PEV of the wapl locus and the sizes of the adjacent heterochromatic blocks carrying the centromere. The smallest PEV-inducing fragment consists of a block corresponding to approximately 10% of Xh and containing the entire XR, the centromere, and a very proximal portion of XL heterochromatin. Heterochromatic blocks retaining the entire XR near the 2E region, but lacking the centromere, show no PEV. Reversion of PEV was also observed as a result of an internal rearrangement of the Xh blocks where the centromere is moved away from the eu-heterochromatin boundary but the amount of X heterochromatin remaining adjacent to 2E is unchanged. We propose a primary role of the X pericentromeric region in PEV induction and an enhancing effect of the other blocks, positively correlated with their size.
Tolchkov
E V
EV
Department of Molecular Genetics of Animals, Institute of Molecular Genetics, Russian Academy of Sciences, Moscow 123182, Russia. teugene@img.ras.ru
Rasheva
V I
VI
Bonaccorsi
S
S
Westphal
T
T
Gvozdev
V A
VA
D000818:Animals; D004331:Drosophila melanogaster / Q000235:genetics*; D005260:Female; D015321:Gene Rearrangement; D008040:Genetic Linkage; D006570:Heterochromatin / Q000235:genetics*; D008297:Male; D014960:X Chromosome; D014998:Y Chromosome
D006570:Heterochromatin