Novel protein interactions and functional analysis of the spliceosome basal complex in Trypanosomes

NATALIA BERCOVICH; SHULAMIT MICHAELI; MARIANO J LEVIN; MARTIN P VAZQUEZ

Bariloche, Argentina

Congreso; Gene expression and RNA processing; 2007

ICGEB-UBA-ANPCyT

Trypanosomes undergo trans-splicing as a major RNA processing event. In this reaction, selection of the 3´splice site AG is not restricted by distance from the branch point-PY. Several analyses revealed distances of AG location from branch point of up to 75 nt. This situation is clearly different from the metazoan cis-splicing in which the PY tract is in its close proximity. These events correlate with the properties of the U2AF heterodimers found in mammals and trypanosomes. While mammalian U2AF heterodimer (U2AF65/U2AF35) forms a strong stable complex that binds the PY-AG together, the trypanosome U2AF complex appeared to be disconnected. In fact, it lost the conserved eukaryote “tongue in groove” interaction and the two subunits only interacted weakly with each other. Moreover, there is no trypanosome consensus for branch-point and it is embedded in the PY tract. This situation correlates with the strong interaction that we observed between U2AF65 (PY recognition) and SF1 (Branch recognition). RNAi knock-down assays showed that trypanosome U2AF35 is an essential protein while U2AF65 and SF1 are conditional essential proteins. Here, we present a model that summarizes the similarities and differences between metazoan and trypanosome organization of the factors involved in early spliceosome assembly.