Multiple interactions are involved in a highly specific association of the Mod(mdg4)-67.2 isoform with the Su(Hw) sites in Drosophila.

Larisa Melnikova,Pavel Georgiev,Anton Golovnin,Margarita Kostyuchenko,Alexander Parshikov,Varvara Molodina

doi:10.1098/rsob.170150

Abstract

The best-studied Drosophila insulator complex consists of two BTB-containing proteins, the Mod(mdg4)-67.2 isoform and CP190, which are recruited to the chromatin through interactions with the DNA-binding Su(Hw) protein. It was shown previously that Mod(mdg4)-67.2 is critical for the enhancer-blocking activity of the Su(Hw) insulators and it differs from more than 30 other Mod(mdg4) isoforms by the C-terminal domain required for a specific interaction with Su(Hw) only. The mechanism of the highly specific association between Mod(mdg4)-67.2 and Su(Hw) is not well understood. Therefore, we have performed a detailed analysis of domains involved in the interaction of Mod(mdg4)-67.2 with Su(Hw) and CP190. We found that the N-terminal region of Su(Hw) interacts with the glutamine-rich domain common to all the Mod(mdg4) isoforms. The unique C-terminal part of Mod(mdg4)-67.2 contains the Su(Hw)-interacting domain and the FLYWCH domain that facilitates a specific association between Mod(mdg4)-67.2 and the CP190/Su(Hw) complex. Finally, interaction between the BTB domain of Mod(mdg4)-67.2 and the M domain of CP190 has been demonstrated. By using transgenic lines expressing different protein variants, we have shown that all the newly identified interactions are to a greater or lesser extent redundant, which increases the reliability in the formation of the protein complexes.

Highlights

The mod(mdg4) gene, known as E(var)3-93D, encodes a large set of protein isoforms with specific functions in the regulation of the chromatin structure of different genes [1,2,3,4,5,6]
Protein isoforms produced by mod(mdg4) contain a common 402 aa N-terminal region encoded by the four 50-exons, but differ in their C-terminal region encoded by alternative 30-exons
The BTB/POZ domain is a conserved protein–protein interaction motif contained in a variety of transcription factors involved in development, chromatin remodelling, insulator activity and carcinogenesis [12,13]

Summary

Introduction

The mod(mdg4) gene, known as E(var)3-93D, encodes a large set of protein isoforms with specific functions in the regulation of the chromatin structure of different genes [1,2,3,4,5,6]. Protein isoforms produced by mod(mdg4) contain a common 402 aa N-terminal region encoded by the four 50-exons, but differ in their C-terminal region encoded by alternative 30-exons. All mRNAs for the alternative Mod(mdg4) isoforms are mainly produced by trans-splicing [7,8,9,10]. The Mod(mdg4) isoforms contain a BTB/POZ domain, an additional dimerization domain and a glutamine-rich (Q) region in the N terminus [1,11]. The BTB domains of the ttk group can multimerize [14], which was suggested to be essential for the ability of the Mod(mdg4) isoforms to support pairing between the distantly located sites in the chromosomes [16]

Methods

Results

Conclusion