Recognition of picornavirus internal ribosome entry sites within cells; influence of cellular and viral proteins.
The ability of different picornavirus internal ribosome entry site (IRES) elements to direct initiation of protein synthesis has been assayed in different cell lines in the presence and absence of viral proteases that inhibit cap-dependent protein synthesis. Reporter plasmids that express dicistronic mRNAs, containing different IRES elements, with the general structure CAT/IRES/LUC, have been assayed. In each plasmid, the CAT sequence encodes chloramphenicol acetyl transferase and the LUC sequence encodes luciferase. The poliovirus (PV) 2A protease and the foot-and-mouth disease virus (FMDV) Lb protease induce the cleavage of the translation initiation factor elF4G and hence inhibit the activity of the cap-binding complex, elF4F. In human osteosarcoma (HTK-143) cells, each of the various IRES elements functioned efficiently. In these cells, the co-expression of the viral proteases severely inhibited the expression of CAT, but the proteases had little effect on the activities of the various IRES elements. In contrast, in baby hamster kidney (BHK) cells, the efficiencies of the different IRES elements varied significantly, whereas, in normal rat kidney (NRK) cells, each of the IRES elements was relatively inefficient. In both BHK and NRK cells, the activities of those IRES elements that functioned inefficiently were strongly stimulated by the co-expression of the PV 2A or FMDV Lb proteases. This stimulation was independent of the loss of cap-dependent protein synthesis and was not achieved by the co-expression of the C-terminal fragment of elF4G. The results suggest that the PV 2A and FMDV Lb proteases induce the cleavage of another cellular protein, in addition to elF4G, which influences IRES function.
Roberts
L O
LO
BBSRC Institute for Animal Health, Woking, Surrey, United Kingdom.
Seamons
R A
RA
Belsham
G J
GJ
D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism*; D004274:DNA, Recombinant; D010450:Endopeptidases / Q000235:genetics / Q000378:metabolism*; D039562:Eukaryotic Initiation Factor-4F; D039603:Eukaryotic Initiation Factor-4G; D006801:Humans; D010442:Peptide Chain Initiation, Translational / Q000235:genetics*; D010448:Peptide Initiation Factors / Q000378:metabolism; D010849:Picornaviridae / Q000201:enzymology / Q000235:genetics*; D012315:RNA Caps / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics; D012367:RNA, Viral / Q000235:genetics*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012270:Ribosomes / Q000378:metabolism; D014764:Viral Proteins
D004274:DNA, Recombinant; D039562:Eukaryotic Initiation Factor-4F; D039603:Eukaryotic Initiation Factor-4G; D010448:Peptide Initiation Factors; D012315:RNA Caps; D012333:RNA, Messenger; D012367:RNA, Viral; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; C057400:picornain 2A, Picornavirus; C088747:leader proteinase, foot-and-mouth disease virus