Component of the gypsy chromatin insulator complex which is required for the function of the gypsy chromatin insulator and other endogenous chromatin insulators. Chromatin insulators are regulatory elements which establish independent domains of transcriptional activity within eukaryotic genomes. Insulators have two defining properties; they can block the communication between an enhancer and a promoter when placed between them and can also buffer transgenes from position effect variegation (PEV). Insulators are proposed to structure the chromatin fiber into independent domains of differing transcriptional potential by promoting the formation of distinct chromatin loops. This chromatin looping may involve the formation of insulator bodies, where homotypic interactions between individual subunits of the insulator complex could promote the clustering of widely spaced insulators at the nuclear periphery. Within the gypsy insulator complex, this protein may control the nature of the repressive effect of su(Hw): in the absence of mod(mdg4) protein, su(Hw) exerts a bidirectional silencing effect, whereas in the presence of mod(mdg4), the silencing effect is unidirectional. Isoform H is specifically required to maintain the pairing of achiasmate homologs in male meiosis I which is mediated by the rDNA repeats on the achiasmate X-Y bivalents. Isoform H also plays a role in apoptotic regulatory pathways. Can self-associate (PubMed:11350941, PubMed:11416154). Interacts with Chi (PubMed:11416154). Interacts with Top2 (PubMed:21304601). Isoform mod2.2: Component of the gypsy chromatin insulator complex, composed of Cp190, mod(mdg4) and su(Hw) (PubMed:7664338, PubMed:11350941, PubMed:11416154, PubMed:15574329). The gypsy chromatin insulator complex interacts with Topors via mod(mdg4) and su(Hw) (PubMed:16209949). Isoform mod2.2 interacts with Trl/GAGA and interaction with this protein may bypass the repressive effects of the su(Hw) insulator (PubMed:15465920). Colocalizes with other elements of the gypsy chromatin insulator complex at multiple sites on polytene chromosomes and at nuclear insulator bodies (PubMed:9491892, PubMed:11106742, PubMed:11350941, PubMed:15574329, PubMed:16209949). The unique C-termini of individual isoforms may specify binding to particular chromosomal locations (PubMed:11350941). During the G2 phase of male meiosis isoform H localizes to the nucleolus (PubMed:16286005). It subsequently localizes to the rDNA repeats of the X-Y bivalent and to multiple autosomal loci, where it remains until anaphase I (PubMed:16286005). Localization to the rDNA repeats requires SA-2, while localization to autosomal loci requires SA-2 and tef (PubMed:16286005). Expressed both maternally and zygotically. Zygotic expression is high in pupae and adult females but low in other stages of development. Homotypic interactions mediated by the BTB (POZ) domain of this protein may promote the clustering of distant insulator complexes into nuclear insulator bodies. C-terminal exons are translated from the opposite DNA strand. This may be due to a trans-splicing event. C-terminal exons are translated from the opposite DNA strand. This may be due to a trans-splicing event. C-terminal exons are translated from the opposite DNA strand. This may be due to a trans-splicing event. C-terminal exons are translated from the opposite DNA strand. This may be due to a trans-splicing event. C-terminal exons are translated from the opposite DNA strand. This may be due to a trans-splicing event. C-terminal exons are translated from the opposite DNA strand. This may be due to a trans-splicing event. C-terminal exons are translated from the opposite DNA strand. This may be due to a trans-splicing event. Intron retention. Intron retention.