User:Sgultyae/Tospovirus IGR structure

Tospovirus IGR structure

The tospovirus IGR structure is a stem-loop RNA structure formed in the intergenic regions (IGR) of RNA segments of tospovirus genome. Such intergenic regions are located between protein-coding regions in the ambisense segments that have two genes in the opposite orientations. Two out of three tospovirus genome segments (S and M segments) are ambisense ones, that is, they encode proteins in both viral RNA (vRNA) sense and its complement, viral-complementary RNA (vcRNA) sense. The L segments encode for proteins in vcRNA sense only. The tospovirus IGR regions contain A-rich and U-rich stretches of nucleotide sequence. These stretches form extended stem-loop RNA structures in both vRNA and vcRNA. The termination of transcription in both orientations occurs just downstream of these stem-loops. Thus, the tospovirus S and M mRNA of both negative (like vRNA) and positive (like vcRNA) sense contain large structures in the 3’ untranslated regions (3’ UTR), formed predominantly by A-U base pairs. These tospovirus IGR structures substitute for the function of the poly(A) tail in translation and may be involved in the regulation of replication and transcription.