Rapid evolution of a recently retroposed transcription factor YY2 in
Chunqing Luoa, Xiaochen Lub, Lisa Stubbsb, Joomyeong Kima,*
aDepartment of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA
bGenome Biology Division, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA
Received 30 June 2005; accepted 10 November 2005
Available online 27 December 2005
YY2 was originally identified due to its unusual similarity to the evolutionarily well-conserved zinc finger gene YY1. In this study, we have
determined the evolutionary origin and conservation of YY2 using comparative genomic approaches. Our results indicate that YY2 is a retroposed
copy of YY1 that has been inserted into another gene locus named Mbtps2 (membrane-bound transcription factor protease site 2). This
retroposition is estimated to have occurred after the divergence of placental mammals from other vertebrates based on the detection of YY2 only in
the placental mammals. The N- and C-terminal regions of YY2 have evolved under different selection pressures. The N-terminal region has
evolved at a very fast pace with very limited functional constraints, whereas the DNA-binding, C-terminal region still maintains a sequence
structure very similar to that of YY1 and is also well conserved among placental mammals. In situ hybridizations using different adult mouse
tissues indicate that mouse YY2 is expressed at relatively low levels in Purkinje and granular cells of cerebellum and in neuronal cells of cerebrum,
but at very high levels in testis. The expression levels of YY2 are much lower than those of YY1, but the overall spatial expression patterns are
similar to those of Mbtps2, suggesting a possible shared transcriptional control between YY2 and Mbtps2. Taken together, the formation and
evolution of YY2 represent a very unusual case where a transcription factor was first retroposed into another gene locus encoding a protease and
survived with different selection schemes and expression patterns.
D 2005 Elsevier Inc. All rights reserved.
Keywords: Retroposition; Evolution; Zinc finger transcription factor
The transcription factor YY1 is a Gli-Kruppel type zinc
finger protein and controls the transcription of a large number
of viral and cellular genes. YY1 can function as a repressor,
activator, or transcriptional initiator depending on the sequence
context of YY1-binding sites with respect to other regulator
elements . The protein has a DNA-binding domain at the
C-terminus and other modulating domains at the N-terminus
displaying repression, activation, and protein-protein interac-
tion activities. YY1 interacts with several key transcription
factors, including TBP, TAFs, TFIIB, and Sp1 [2,4,12,20,23].
Other studies also indicated that YY1 recruits histone-modify-
ing enzymes including p300, HDACs, and PRMT1 for
transcription control [13,17,25]. Physiological roles for
YY1have been demonstrated in mouse by gene knockout
experiments, in which homozygous mutant mice show peri-
implantation lethality and a subset of heterozygous mice show
developmental abnormalities, such as excenphaly (or open
YY1 is evolutionarily well conserved throughout all verte-
brate lineages although no systematic and comprehensive
studies to date have addressed the evolutionary history of this
gene. At least two genes similar to vertebrate YY1 are found
even in fly, and one of them is known to be involved in a
heritable silencing mechanism as a component of the Polycomb
complex . Many key transcription factors, including Sp1 and
E2F, have evolutionary histories similar to that of YY1. These
0888-7543/$ - see front matter D 2005 Elsevier Inc. All rights reserved.
iSequence data from this article have been deposited with the EMBL/
GenBank Data Libraries under Accession No. DQ107161.
iiThe U.S. Government’s right to retain a nonexclusive royalty-free
license in and to the copyright covering this paper, for governmental purposes,
* Corresponding author. Fax: +1 225 578 2597.
E-mail address: email@example.com (J. Kim).
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