1022-7954/04/4002- © 2004
Russian Journal of Genetics, Vol. 40, No. 2, 2004, pp. 193–196. Translated from Genetika, Vol. 40, No. 2, 2004, pp. 256–260.
Original Russian Text Copyright © 2004 by Muravenko, Amosova, Samatadze, Semenova, Nosova, Popov, Shostak, Zoschuk, Zelenin.
At present, ﬂuorescence in situ hybridization
(FISH) is the most illustrative method to physically
localize the 5S and 45S ribosomal genes on chromo-
somes of various species. Employed in genome analy-
sis of commercially valuable plant species and their
wild relatives, this method permits more exact chromo-
some identiﬁcation and mapping, demonstrates the
relatedness of individual species, and elucidates their
phylogenetic relationships [1–4]. However, FISH has
been used only scarcely, if at all, to study the chromo-
somes of cultivated ﬂax, an important species in Russia,
and of related wild species.
It is known that, in most eukaryotes, rRNA genes
are usually clustered in tandem repeats and located on
one or a few chromosomes. The 18S–5.8S–25.5S (45S)
and 5S rDNA sequences are separated by variable non-
coding regions in such clusters [5–7].
Analysis of the rRNA genes in cultivated ﬂax
= 30) revealed a substantial varia-
tion in their copy number per genome [8, 9]. Studies of
the ribosomal gene structure in a cultivated ﬂax acces-
sion showed that the 18S–5.8S–25.5S (45S) rDNA is a
8.6-kb homogeneous unit consisting of tandem repeats
(approximately 2400 copies per diploid nucleus) with
highly variable intergenic spacers [10, 11].
5S ribosomal genes are clus-
tered to form tandem repeats with a repetitive unit of
350–370 bp, including a 120-bp transcribed region and
a 230-bp spacer [12, 13]. The 5S rRNA genes account
for approximately 3% of the cultivated ﬂax genome,
and the 5S rDNA copy number in genotrophs varies
from 49 600 to 117 000 per diploid genome and shows
no correlation with the copy number of the 18S–25S
ribosomal genes [10, 13, 14].
Attempts to localize the ribosomal genes on
chromosomes yielded ambiguous results
[11, 14–17, 19].
Judging from the available published data, wild ﬂax
species were not examined with respect to the molecu-
lar structure of the ribosomal genes. We have recently
started a study of nucleolus-organizing chromosome
regions of wild ﬂax species [18, 19].
In this work, we used FISH to study the chromo-
somal location and colocalization of the 5S and 45S
rDNA in the genomes of cultivated ﬂax and four wild
ﬂax species of the section
Chromosome Localization of 5S and 45S Ribosomal DNA
in the Genomes of
L. Species of the Section
O. V. Muravenko, A. V. Amosova, T. E. Samatadze, O. Yu. Semenova, I. V. Nosova, K. V. Popov,
N. G. Shostak, S. A. Zoschuk, and A. V. Zelenin
Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, 119991 Russia;
fax: (095)135-14-05; e-mail: firstname.lastname@example.org
Received August 22, 2003
—Fluorescence in situ hybridization (FISH) was for the ﬁrst time used to study the chromosomal loca-
tion of the 45S (18S–5.8S–26S) and 5S ribosomal genes in the genomes of ﬁve ﬂax species of the section
= 30), and
= 30), a major hybridization site of 45S rDNA was observed in the pericentric region of a
large metacentric chromosome. A polymorphic minor locus of 45S rDNA was found on one of the small chro-
mosomes. Sites of 5S rDNA were colocalized with those of 45S rDNA, but direct correlation between signal
intensities from the 45S and 5S rDNA sites was observed only in some cases. Other 5S rDNA sites mapped to
two chromosomes in these ﬂax species. In
= 16) and
= 18), large
regions of 45S and 5S rDNA were similarly located on a pair of homologous satellite-bearing chromosomes.
An additional large polymorphic site of 45S and 5S rDNA was found in the proximal region of one arm of a
small chromosome in the
L. usitatissimum, L. angustifolium
karyotypes. The other arm of this
chromosome contained a large 5S rDNA cluster. A similar location of the ribosomal genes in the pericentric
region of the pair of satellite-bearing metacentrics conﬁrmed the close relationships of the species examined.
The difference in chromosomal location of the ribosomal genes between ﬂax species with 2
= 30 and those
= 16 or 18 testiﬁed to their assignment to different sections. The use of ribosomal genes as chromosome
markers was assumed to be of importance for comparative genomic studies in cultivated ﬂax, a valuable crop
species of Russia, and in its wild relatives.