ISSN 1022-7954, Russian Journal of Genetics, 2016, Vol. 52, No. 10, pp. 1007–1014. © Pleiades Publishing, Inc., 2016.
Original Russian Text © O.V. Kyrchanova, D.V. Leman, S.V. Toshchakov, M.V. Utkina, M.V. Tikhonov, A.F. Parshikov, O.G. Maksimenko, P.G. Georgiev, 2016, published in Genetika,
2016, Vol. 52, No. 10, pp. 1117–1125.
Induction of Transcription through the scs Insulator Leads
to Abnormal Development of Drosophila melanogaster
O. V. Kyrchanova*, D. V. Leman, S. V. Toshchakov, M. V. Utkina, M. V. Tikhonov,
A. F. Parshikov, O. G. Maksimenko, and P. G. Georgiev
Institute of Gene Biology, Russian Academy of Sciences, Moscow, 119334 Russia
Received December 28, 2015; in final form, March 4, 2016
Abstract—A regulatory element named scs is one of the first insulators discovered in Drosophila, which was
found on the boundary of the hsp70 domain. The 993-bp scs insulator contains two promoters at the ends and
two polyadenylation signals located in the same orientation in the central part of the insulator. In the Dro-
sophila transgenic lines, induction of a strong transcription through the scs insulator only in the direction that
coincides with the direction of the two polyadenylation sites activity results in multiple phenotypic defects of
the Drosophila development and embryonic lethality. A similar effect was not observed upon testing of other
known Drosophila insulators.
Keywords: transcription, insulator, UAS, polyadenylation signal, T-effect
In higher eukaryotes, an enhancer can activate a
promoter at a distance of up to several hundred
kilobases . The study of insulators is essential to
understand the mechanisms regulating the long-dis-
tance interactions between the regulatory elements.
Insulators are the regulatory elements that block the
interaction between the enhancer and promoter [2–4].
Moreover, insulators do not directly affect the activity
of the enhancer and promoter; i.e., a promoter may be
activated by any other enhancer and an enhancer can
activate any other promoter. Insulators were discov-
ered and most thoroughly studied in the fruit fly Dro-
sophila melanogaster [2–4].
The first insulators were found at the boundaries of
the two hsp70 genes [5, 6]. They were named scs and
scs' (specialized chromatin structure), as their associ-
ation with the nuclear matrix was expected. Analysis of
the properties of scs and scs' insulators in the trans-
genic lines made it possible to formulate the two main
criteria on which the analyzed regulatory element can
be assigned to the insulators: the ability to block
enhancers and to be a barrier between the active and
condensed chromatin [6, 7].
The scs and scs' insulators are located in the 87A7
cytogenetic locus of chromosome 3 [7, 8]. These insu-
lators flank the region including two heat shock hsp70
(heat shock protein 70) genes and the CG31211 and
CG3281 genes (Fig. 1). Moreover, the scs insulator
contains the CG31211 and Cad87A promoters. Inter-
estingly, the Cad87A promoter is expressed at all stages
of development, and in contrast to most known RNA
polymerase II-dependent promoters, its activity is not
regulated by a strong yeast GAL4 activator [9, 10]. The
scs' insulator also contains two promoters, CG3281
In the structure of scs insulator, three regions pro-
viding an enhancer-blocking activity can be identified.
These fragments do not have considerable homology
between each other at the DNA sequence, but are
functionally equivalent and, complementing each
other, are involved in the insulation [11, 12]. Each of
these regions separately is characterized by a weaker
enhancer-blocking capability compared with the full-
length scs insulator. However, the strength of the full-
length scs insulator can be achieved by multimeriza-
tion of any of these regions.
The characterized protein component of the scs
insulator is the Scs-binding protein (SBP, Zw5),
encoded by the zeste-white 5 (zw5) gene. It contains
eight zinc fingers and binds the DNA sequence of
24 bp located next to the CG31211 promoter [12, 13].
Other scs insulator proteins have not yet been discov-
ered. It was demonstrated that the scs insulator or the
Zw5 protein binding sites were able to maintain distant
interactions in the transgenic Drosophila models .
The scs' insulator is much weaker than scs and con-
tains binding sites for the BEAF transcription factor
[15, 16]. In the transgenic Drosophila models, it was
demonstrated that functional interaction between the
scs and scs' insulators led to the increased enhancer-
blocking activity of the scs' insulator .