Abstract
The formation of interphase chromosomes is a multi-level process in which DNA is compacted several thousandfold by association with histones and non-histone proteins. The first step of compaction includes the formation of nucleosomes – the basic repeating units of chromatin. Further packaging occurs due to DNA binding to histone H1 and non-histone proteins involved in enhancer-promoter and insulator interactions. Under these conditions, the genome retains its functionality due to the dynamic and uneven DNA compaction along the chromatin fiber. Since the DNA compaction level affects the transcription activity of a certain genomic region, it is important to understand the interplay between the factors acting at different levels of the packaging process. Drosophila polytene chromosomes are an excellent model system for studying the molecular mechanisms that determine DNA compaction degree. The unevenness of DNA packaging along the chromatin fiber is easily observed along these chromosomes due to their large size and specific banding pattern. The purpose of this study was to figure out the role of two non-histone regulatory proteins, ADF1 and BEAF-32, in the DNA packaging process from nucleosome positioning to the establishment of the final chromosome structure. We studied the impact of mutations that affect ADF1 and BEAF-32 binding sites on the formation of 61C7/C8 interband – one of the decompacted regions of Drosophila polytene chromosomes. We show that such mutations led to the collapse of an interband, which was accompanied with increased nucleosome stability. We also find that ADF1 and BEAF-32 binding sites are essential for the rescue of lethality caused by the null allele of bantam microRNA gene located in the region 61C7/C8.
Highlights
Eukaryotic DNA is organized in a compact nucleoprotein complex called chromatin
We showed that ADF1 and BEAF-32 localized to the 61C7/C8 interband in salivary gland polytene chromosomes (Berkaeva et al, 2009)
In this study, we investigated the role of non-histone regulatory proteins ADF1 and BEAF-32 in the positioning of nucleosomes and formation of 61C7/C8 interband – one of the decompacted regions of Drosophila polytene chromosomes
Summary
Eukaryotic DNA is organized in a compact nucleoprotein complex called chromatin. Nucleosome arrays form a so-called “10-nm fibril” which is further folded into higher order chromatin structures by histone H1 and a large number of functionally different non-histone proteins. Nucleosome positioning determines the availability of DNA for the binding of non-histone proteins that regulate transcription and replication. Non-histone proteins affect nucleosome positioning: they can destroy a nucleosome by displacing histone octamer or recruit ATP-de pendent remodeling complexes that move the nucleosomes along the chromosomes. Nucleosome arrays are thought to self-organize against the potential barrier introduced by DNA-bound non-histone protein complexes due to the steric exclusions between adjacent nucleosome particles (Chereji et al, 2016; Chereji, Clark, 2018)
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