ISSN 10227954, Russian Journal of Genetics, 2010, Vol. 46, No. 8, pp. 924–931. © Pleiades Publishing, Inc., 2010.
Original Russian Text © A.S. Kagramanova, T.V. Kapelinskaya, A.L. Korolev, D.V. Mukha, 2010, published in Genetika, 2010, Vol. 46, No. 8, pp. 1041–1049.
The R1 retroposons are sitespecific mobile ele
ments (ME) of eukaryotes, whose transposition occurs
within the ribosomal gene cluster. These ME contain
two open reading frames (ORFs). The protein corre
sponding to ORF1 is homologous to GAG protein of
retroviruses, while the protein corresponding to ORF2
plays a key role in the process of transposition [1, 2]. It
was demonstrated that integration of R1 retroposons
occurs into certain target site of the 28S rRNA gene,
which results in inactivation of this gene copy [3–5].
In the genomes of a number of organisms, several
retroposon subfamilies with similar target sites, but
displaying different degrees of differences in nucle
otide composition, were described. For instance, in
the genome of fruit fly
retroposon R1 subfamilies , while in the genome of
, at least four retroposon
R2 subfamilies are identified .
The appearance of several ME subfamilies in one
genome can be caused by horizontal transfer .
However, the existence of closely relative subfamilies
of R1 retroposons with similar structure and nucle
otide sequences clearly points to the possibility of
intragenomic divergence of this type of mobile ele
ments. Because of this, these mobile elements can
serve as convenient model to study the patterns of
molecular evolution of eukaryotic genome as a whole.
In our earlier studies, cloning and amplification of
different variants of 5' truncated copies of R1 retro
posons from the genomic DNA of German cockroach
was performed. Sequence compar
ison of the clones obtained provided identification of
two subfamilies of this retroposon in German cock
In the present study, a library of German cockroach
genes constructed with the help of cosmid vector, was
screened with the probes generated using cloned frag
ments of 5'truncated copies of two subfamilies of R1
retroposons. Fulllength copies of retroposons of
interest were identified and partly sequenced. It was
demonstrated that in German cockroach, retroposons
R1, belonging to different subfamilies, differed from
one another in domain structure of the Cterminal
region of the second reading frame. For the first time,
in the sequence of retroposon R1 transmembrane
domains were detected.
MATERIALS AND METHODS
Cloning and sequencing.
A genomic library of Ger
man cockroach was generated using the SuperCos I
(Stratagene) cosmid vector, according to the recom
mendations of the manufacturer. Clones containing
recombinant DNA were screened with radioactively
labeled probes, represented by the fragments (about
1000 bp) of 5'truncated copies of the two subfamilies
of retroposons R1, described earlier . The assign
ment cloned mobile elements to one or another sub
family types, as well as their fulllength was endorsed
by sequencing of the ME flanking regions. Integrated
copies of retroposons were attributed to native (full
length) copies in case of identification of extended 5'
untranslated regions. Determination of extended 5'
and 3' terminal sequences of mobile elements exam
ined was performed using the method of stepwise
Domain Organization of the ORF2 CTerminal Region
of the German Cockroach Retroposon R1
A. S. Kagramanova, T. V. Kapelinskaya, A. L. Korolev, and D. V. Mukha
Vavilov Institute of General Genetics, Russian Academy of Sciences, Moscow, 119991 Russia;
Received February 16, 2010
—Using cosmid vector, a gene library of German cockroach
From this library, clones containing fulllength copies of two subfamilies of R1 retroposons were selected.
Retroposons R1 of German cockroach belonging to different subfamilies were shown to be different in
domain organization of the ORF2 Cterminal region. For the first time, retroposons transmembrane domains
were identified in the sequences of R1. It was demonstrated that two retroposon R1 subfamilies of German
cockroach arose as a result of intragenomic divergence rather than via horizontal transfer of alien mobile ele
ment into cockroach genome. The differences in domain organization appeared not as a result of saltatory
recombination processes, but as a consequence of gradual mutation accumulation, which led to either degen
eration, or to domain formation.