Nucleic Acids Research, Vol 24, Issue 12 2338-2346, Copyright © 1996 by Oxford University Press
AM Hug and H Feldmann
The retrotransposon Ty4 is found in different yeast strains at only one to
three copies per haploid genome. In the present study, we aimed at relating
the apparent low transpositional activity of Ty4 to transcriptional
features of this element. RT-PCR revealed that Ty4 is transcribed at a very
low level, being comparable with that of GAL4. Contrary to other Ty
elements, the transcriptional rate of Ty4 is not affected in a sin4
background nor by treatment of cells with alpha factor. From experiments
measuring the expression levels in 1acZ fusion constructs, we conclude that
Ty4 transcription is repressed by a negative regulating element residing
within the LTR, whereas positive cis-acting elements, like those that have
been found to mediate expression of Ty1/2 and Ty3, are absent from Ty4.
Analysing Ty4 transcript termini by the RACE-PCR method, we found several
distinct transcriptional initiation sites. But surprisingly, the majority
of the polyadenylated Ty4 transcripts terminate shortly upstream from the
3' LTR boundary, so that these transcripts do not contain a U3-R sequence,
which is normally required for obligate strand transfer during DNA
synthesis. Thus, the extremely low transcription rate of Ty4 and imperfect
Ty4 transcripts are the reason for the low transpositional activity of this
element.
ARTICLES
Yeast retrotransposon Ty4: the majority of the rare transcripts lack a U3-R sequence
Institut Fur Physiologishce Chemie, Physikalische Biochemie und Zellbiologie der Universitat Munchen, Germany.
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