1022-7954/03/3909- $25.00 © 2003
Russian Journal of Genetics, Vol. 39, No. 9, 2003, pp. 1013–1020. Translated from Genetika, Vol. 39, No. 9, 2003, pp. 1203–1211.
Original Russian Text Copyright © 2003 by Markov, Zakharov, Galkin, Strunnikov, Smirnov.
Dynamics of the chromatin structure is currently
known to be dependent on two DNA-binding protein
complexes: condensin and cohesin (from cohesion).
Both complexes include SMC (structure maintenance
of chromosomes) proteins responsible for binding with
DNA. Condensin controls the linear organization of
chromosomes, whereas cohesin ensures proper chro-
matid segregation immediately after the DNA replica-
tion and until the onset of division. According to some
data, cohesion is required for recombination repair.
Several proposed models of chromosomes are based on
a balance between cohesin and condensin complexes
bound with DNA [1–3].
As shown for lower eukaryotes, at least four major
subunits are required for the formation of a functional
cohesin complex. Two subunits, Smc1 and Smc3,
belong to the SMC family and form a heterodimer that
directly binds to DNA via two ATP-dependent
domains. Each of these heterodimers seems to interact
with one of the sister DNA stands . The two other
subunits, Scc1 and Scc3 (sister chromatid cohesion),
also form a heterodimer, which regulates the operation
of the complex and the cohesion of the sister chroma-
tids. The Scc1–Scc3 heterodimer “pulls together” two
heterodimers Smc1/Smc3 connected to the sister chro-
matids [2, 5].
Removing the cohesin complex from yeast chromo-
somes is a one-step event, whereas in frog, this is a two-
step process. Different types of SA (stromal antigen)
proteins, which are homologous to yeast Scc3 (SA1 and
SA2), and their stage-speciﬁc phosphorylation may
account for this difference. In yeast and higher eukary-
otes, the second stage of the cohesin complex removal
is executed by the proteolytic enzymatic separin–
securin system controlled by APC (anaphase promoting
is an organism convenient
for studying the mechanisms of sister chromatid inter-
is thoroughly studied by
genetic and cytogenetic methods. In this organism, a
number of mutations were described responsible for
cohesion and some cohesin components [8–12]. In
addition, homologs for major cohesin proteins of
higher eukaryotes were found in
DRAD21p protein is a structural and functional homo-
logue of Scc1 protein and probably has similar functions,
but this was been conﬁrmed experimentally [11–13].
proved to be a unique
object for studying cohesion in interphase nuclei. The
presence of polytene chromosomes in
makes it possible to observe sister chromatid interac-
tion at the cytological level and describe the develop-
ment of the cohesin complex.
It is of interest to elucidate the correlation between
cohesion protein binding and the degree of chromatin
compaction, because cohesion is observed during the
entire synthetic stage and in the G
phase. We used the
polytene chromosome model to examine the differen-
tial cohesin distribution in interphase chromosomes.
MATERIALS AND METHODS.
Preparations of salivary gland polytene chromo-
somes and neuroblast interphase nuclei for immun-
We used neural ganglia for mitotic chromo-
Cohesin Complexes in Polytene Chromosomes
Are Located in Interbands
A. V. Markov
, A. A. Zakharov
, A. P. Galkin
, A. V. Strunnikov
, and A. F. Smirnov
St. Petersburg State University, St. Petersburg, 199034 Russia;
fax: (812) 328-05-41; e-mail: email@example.com; Aleksandr.Smirnov@paloma.spbu.ru
National Institute of Health, NICHD, Unit of Chromosome Structure and Function, Bethesda, United States;
Received January 9, 2003
—The distribution of cohesin complex in polytene chromosomes of
studied. Cohesin is a complicated protein complex which is regulated by the DRAD21 subunit. Using immun-
ostaining for DRAD21p, the cohesins were shown to be preferentially located in the interband regions. This
speciﬁcity was not characteristic for puffs, where uniform staining was observed. The presence of a few brightly
ﬂuorescent regions (ﬁve to ten per chromosome arm) enriched with cohesin complexes was shown. Some of
these regions had permanent location, and the others, variable location. No antibody binding was detected in
the chromocenter. Immunostaining of interphase nuclei of neuroblasts revealed large cohesin formations. On
the polytene chromosomes of
gene was mapped to the chromocentric region (81)
of the L arm of chromosome 3.