LAUSR

TRF2 protein (TBP-related factor 2) can substitute for TBP forming alternative transcription initiation complexes on TATA-less promoters, including the promoters of histone H1 and piRNA clusters required for transposon repression. The Drosophilatrf2 gene codes for two isoforms: a “short” and a “long” one, in which the same short TRF2 sequence is preceded by a long N-terminal domain. Here, we demonstrated that the long TFR2 isoform has a greater functional activity than the short isoform by expressing each of them at a reduced rate under the endogenous promoters. Expression of the long isoform alone affects neither the flies’ viability nor the sex ratio. Expression of the short isoform alone leads to the phenotype described for the trf2 gene insufficiency and derepression of transposable elements, that is, decreased viability, disturbance of homologous chromosome pairing and segregation, and apparent female-biased sex ratio.