Specific mRNP complexes

Abstract

These studies were designed to identify the proteins associated with specific mRNAs. L6 myoblasts contain a unique poly(A)-rich H4 mRNA as well as poly(A)-minus H4 mRNA subspecies. We have characterized the proteins present in both poly(A)-rich and poly(A)-minus histone H4 mRNP complexes following ultraviolet crosslinking in vivo. In addition. the muscle-specific myosin heavy chain (MHC) mRNP complex was characterized in myoblasts.[35S]Methionine-labelled poly(A)-rich and poly(A)-minus RNP complexes were prepared from both the polysomal and free (post-polysomal) RNP compartments. From each fraction the mRNP encoding histone H4 or MHC was purified by hybrid selection to a cloned human histone H4 gene or MHC cDNA. A unique set of 6 -16 proteins was found bound to each of the specific mRNP complexes. These proteins were a subset of the total population of either polysomal or free RNP proteins and some proteins appeared common among the different hybrid-selected RNP fractions. The results demonstrate that (a) mRNAs bind a different set of proteins depending upon whether they are present in the polysomal or free mRNP fraction; (b) the presence of poly(A) sequences affects the proteins which bind to H4 mRNA in the free RNP compartment.

Translation of poly(A)-binding protein mRNA is regulated by growth conditions

“…More recently the proteins interacting with unique RNA sequences have been increasingly investigated. Earlier studies utilized the method of hybrid selection to identify proteins associated with several mRNA species (Johnson and Ilan 1982;Ruzdijic et al 1984Ruzdijic et al , 1985. An alternative method of identifying proteins binding to specific mRNAs is to reconstitute mRNPs in vitro using defined RNA sequences.…”

“…The proteins associated with the global population of mRNA in the cytoplasm have been extensively investigated, resulting in the identification of a family of proteins which may be described as general mRNA binding proteins (Greenberg 1979;Wagenmakers et al 1980;Ruzdijic et al 1984;Greenberg and Carroll 1985;Ruzdijic et al 1985). The most thoroughly investigated of the general mRNA-associated proteins is PABP.…”

Proteins associated with the messenger ribonucleoprotein particle for the estrogen-regulated apolipoprotein II mRNA

“…Formaldehyde-fixed apoll mRNP had an average density of 1.4 g/mL, corresponding to a particle composition of 15% protein/25% RNA by weight. This composition is typical of bulk mRNP as well as the few specific mRNPs that have been examined (Dreyfuss, 1986;Ruzdijic et al, 1985;Preobrazhensky & Spirin, 1978;Greenberg, 1977). Fractionation of liver polyribosomes and mRNP on successive sucrose gradients yielded a 7-fold enrichment of apoll mRNP relative to other mRNPs.…”

“…It is of interest that previous studies found no striking differences between the mRNP proteins cross-linked to bulk cellular mRNA in different cell types grown in culture (Greenberg, 1980;Dreyfuss et al, 1984;Dreyfuss, 1986) or in the highly specialized reticulocyte (Greenberg & Carroll, 1985). Similarly, in vesicular stomatitis virus infected cells, where viral message becomes the predominant mRNA on treatment of cells with actinomycin D (Dreyfuss et al, 1984), in polyadenylated histone H4 mRNAs (Ruzdijic et al, 1985), or in proteins cross-linked to mRNAs microinjected into Xenopus oocytes (Swiderski & Richter, 1988), an identical pattern of mRNP proteins was detected by cross-linking. These findings, as well as the results of the present study, suggest that the major mRNP proteins associated with EDTA-released mRNP and detected by UV cross-linking are common to many cellular mRNAs, and likely participate in aspects of mRNA metabolism common to most mRNAs.…”