Signal Manager :: View

r1={au,ua,gc,cg,gu,ug}
p1=gg g p2=u p3=gyyug 5...50 r1~p3 ugagaa[1,0,0] r1~p2 gu r1~p1 cuuugaa[2,0,0]  p4=ccu gan p5=cagg[1,0,0] ruaaur[2,0,0] r1~p5 cgn r1~p4 ga gugugc[1,0,0] 

The 3' region of the thiamine biosynthesis gene THIC contains a riboswitch aptamer (i.e. a RNA motif adopting alternate structures depending on  the binding of a metabolite) sensing the thiamine pyrophosphate (TPP) concentration. In some plant species the TPP riboswitch has been also found in THI1, another gene of thiamin biosynthesis.The TPP riboswitch, whose structure has been confirmed by crystal structure resolution (Thore et al. 2006), consists of five helices, termed P1 to P5, and has a consensus length of 116 nt. The TPP riboswitch controls THIC splicing in response to changes in TPP levels. In Arabidopsis thaliana, it has been shown (Wachter et al., 2007) that when TPP concentration is low a complementary interaction between the TPP aptamer and the 5' splicing site of the second intron located in the 3'UTR of THIC pre-mRNA prevents splicing and gives rise to a mature transcript containing a shorter 3'UTR, not containing the riboswitch sequence, that permits high expression. On the contrary, when TPP concentration is high the binding of TPP to the riboswitch aptamer leads to a structural change that prevents its interaction with the 5' splicing site. Therefore the splicing occurs and generates a mature transcript with a longer 3'UTR including most of the riboswitch consensus but the first seven nt that reduces THIC expression  possibly through increased transcript turnover. The regulation of thiamine biosynthesis involving the TPP riboswitch is  conserved in all life kingdoms even if adopts a variety of mechanisms (Bocobza et al., 2007)