Position effect variegation (PEV) is a disturbance of the expression of euchromatic genes transferred into the heterochromatin vicinity caused by the changes in its chromatin organization (heterochromatinization). Little is known about the molecular mechanisms of interactions between gene transcription machinery and the large-scale chromatin structures like heterochromatin, and the chromosomal rearrangement In(2)A4 provide a convenient model to study PEV. The aim of our work was to track the changes in chromatin organization of euchromatin in the vicinity of In(2)A4 new eu-heterochromatin borders and analyze the possible correlations between chromatin changes and the functional organization of the affected regions. Methods: We’ve performed analysis of genome-wide HP1a distribution in In(2)A4/In(2)A4 homozygous flies and in the control wild type flies by ChIP-Seq with qPCR verification and bioinformatic analysis of the received data. Results: In(2)A4 rearrangement is an inversion in the left arm of chromosome 2 with a breakpoint in the satellite block in the 2L pericentromeric heterochromatin. This results in two new eu-heterochromatin boundaries – one near the main block of 2L heterochromatin and another one near the separated small heterochromatin block. ChIP-Seq data on HP1a distribution shows an enrichment for HP1a in the euchromatin regions near the new eu-heterochromatin borders. HP1a spreads up to 200 kb from the main pericentromeric block and up to 50 kb from the small block. No apparent correlation between HP1a enrichment and genes expression levels (studied in [1]) or gene amenability to PEV were detected. The unusual enrichment in HP1a immediately near the small separated heterochromatin block was observed. Conclusions: In In(2)A4, HP1a propagates at a distance of up to 200 kb from the breakpoints and there is no apparent correlation between HP1a enrichment and expression levels of genes in the affected region as well as no correlation between HP1a binding and sensitivity of any particular gene to heterochromatin repression. It seems that HP1a propagation occurs independently of local chromatin organization defined by regulatory elements. Funding: This work is supported by RFBR (grants 17-04-01984, 17-00-00282) and RSCF 19-74-20178 References 1. Abramov, Y.A., et al., The Differences Between Cis- and Trans-Gene Inactivation Caused by Heterochromatin in Drosophila. Genetics, 2016. 202(1): p. 93-106.