De. Cryderman et al., Characterization of sequences associated with position-effect variegation at pericentric sites in Drosophila heterochromatin, CHROMOSOMA, 107(5), 1998, pp. 277-285
In a variety of organisms, euchromatic genes brought into juxtaposition wit
h pericentric heterochromatin show position-effect variegation (PEV), a sil
encing of gene expression in a subset of the cells in which the gene is nor
mally expressed. Previously, a P-element mobilization screen identified tra
nsgenic Drosophila stocks showing PEV of an hsp70-white(+) reporter gene; t
ransgenes in many of these stocks map to the chromocenter of polytene chrom
osome. A screen at an elevated temperature identified two stocks that under
standard culture temperatures show complete repression of the hsp70-white transgene. The transgenes in both cases map to the chromocenter of polyten
e chromosomes. Different types of middle repetitive elements are adjacent t
o seven pericentric transgenes; unique sequences are adjacent to two of the
perimetric transgenes. All of the transgenes show suppression of PEV in re
sponse to a mutation in the gene encoding heterochromatin protein 1 (HP1).
This suppression correlates with a more accessible chromatin structure. The
results indicate that a pericentric transgene showing PEV can be associate
d with different types of DNA sequences, while maintaining a common associa
tion with the chromosomal protein HP1.