Functional characterisation of the Schizosaccharomyces pombe homologue of the leukaemia-associated translocation breakpoint binding protein translin and its binding partner, TRAX

Abstract

Translin is a conserved protein which associates with the breakpoint junctions of chromosomal translocations linked with the development of some human cancers. It binds to both DNA and RNA and has been implicated in mRNA metabolism and regulation of genome stability. It has a binding partner, translin-associated protein X (TRAX), levels of which are regulated by the translin protein in higher eukaryotes. In this study we find that this regulatory function is conserved in the lower eukaryotes, suggesting that translin and TRAX have important functions which provide a selective advantage to both unicellular and multi-cellular eukaryotes, indicating that this function may not be tissue-specific in nature. However, to date, the biological importance of translin and TRAX remains unclear. Here we systematically investigate proposals that suggest translin and TRAX play roles in controlling mitotic cell proliferation, DNA damage responses, genome stability, meiotic/mitotic recombination and stability of GT-rich repeat sequences. We find no evidence for translin and/or TRAX primary function in these pathways, indicating that the conserved biochemical function of translin is not implicated in primary pathways for regulating genome stability and/or segregation.

Translin and Trax differentially regulate telomere-associated transcript homeostasis

“…Despite this, deletion of both the Translin ( tsn1 + ) and Trax ( tfx1 + ) genes of the fission yeast Schizosaccharomyces pombe does not result in any readily detectable phenotypic change [35, 36]. Given the finding that Translin and Trax regulate RNA dynamics in other organisms, we set out to determine whether S. pombe Tsn1 and Tfx1 are involved in transcript regulation.…”

“…Not only is the elevation of the tlh transcripts the first measurable phenotype of a tfx1 Δ mutant, it also reveals a functional separation between Tfx1 and Tsn1 in S. pombe. S. pombe Tsn1 functions to stabilize Tfx1 [35] and in the absence of Tsn1 there are considerably reduced levels of Tfx1 [35]. The tlh transcript data indicate that the low levels of Tfx1 in the tsn1 Δ background remain sufficient to maintain tlh transcript repression.…”

“…Previously, it has been demonstrated that mouse Trax can inhibit the binding of mouse Translin to mRNA [53], and a similar direct regulation might be occurring here to drive the inter paralogue modulation mechanism. Additionally, when tsn1 + is mutated, Tfx1 levels become depleted [35], so the residual Tfx1 found in the tsn1 + mutant must be sufficient to maintain a functional role for telomere transcript level regulation.…”

Recombination at DNA replication fork barriers is not universal and is differentially regulated by Swi1

“…The fission yeast RTS1 element is a polar RFB, and previous work has demonstrated it can function as a polar, intrachromatid mitotic recombination hotspot (27). To test whether a single RTS1 RFB can drive intermolecular homologous recombination, we established a plasmid-by-chromosome recombination reporter system based on a system we have used previously (33). Briefly, we introduced the RTS1 element into the ORF of the S. pombe ade6 gene at the BstXI site (Fig.…”

Rgf1p (Rho1p GEF) is required for double-strand break repair in fission yeast

“…We employed a NHEJ plasmid recircularization assay (43). Plasmid pFY20 was linearized using restriction endonucleases which generate 5΄ over hangs (XmaI), 3΄ over hangs (PstI) or blunt termini (SmaI); these linear plasmids are then transformed into cells and the transformation frequency was used to measure the efficiency of plasmid recircularization.…”