Host proteins are associated with adenovirus specific mRNA in the cytoplasm

Abstract

In eukaryotic cells mRNA and its precursors are always associated with proteins to form ribonucleoprotein complexes. The major protein components present in isolated cytoplasmic mRNAprotein complexes have Mr of approximately 73 000 and 52 000. The larger protein has been shown to be associated with the poly(A)-region of cytoplasmic mRNA [ 1,2]. Although there probably are more mRNA-associated proteins, the published reports on their variations and diversity remain a matter of considerable dispute. One reason for the reported discrepancies is the fact that the methods used to isolate mRNP complexes have the acknowledged disadvantage that non-specific binding of proteins to the RNA during cell fractionation may occur. On the other hand, conditions which minimize non-specific adsorption mostly promote dissociation of messenger-associated proteins from the RNA. Another problem is created by the fact that some proteins present in mRNP particles might not be directly associated with the RNA but, for example, via protein-protein interactions. Particular difficulties arise when viral mRNA-protein complexes have to be purified from mixtures in which host mRNP complexes are present as well. Reliable separations between viral and host mRNA-protein complexes have never been carried out. Thus, most reports on the composition of viral mRNA-protein particles focused on differences in the composition of viral and host complexes [3-51. We have used cross-linking in vivo by means of