Rat liver nuclear skeleton and ribonucleoprotein complexes containing HnRNA.

Abstract

Rat liver nuclei deprived of chromatin and nucleoplasm show a spongelike network which preserves its connection with nucleoli, the inner membrane of the nuclear envelope, and nuclear pore complexes. It contains all of the HnRNA, provided the endogenous proteolytic activity is inhibited by a proteolytic inhibitor such as phenylmethyl sulfonyl chloride (PMSC) or the fluoride form (PMSF). In the absence of these proteolytic inhibitors, HnRNA is dissociated from the spongelike network and sediments in a sucrose gradient as polydispersed ribonucleoprotein complexes. Furthermore, purified HnRNA as well as rRNA do not bind to the spongelike network when added to these nuclei. These observations demonstrate that the association of HnRNA to the nuclear skeleton is not an artifact. RNase treatment of the spongelike network digests the majority of the rapidly labeled RNA but does not alter the morphological aspect nor the architecture of this network. EDTA and heparin treatments affect neither the attachment of HnRNA nor the structural organization of this network. Electron microscope studies of the network reveal a characteristic flexuous configuration. Its relationship with diffused and condensed chromatin is discussed. KEY WORDS nuclear skeleton proteases 9 ribonucleoprotein complexes 9 heterogeneous RNA nudeal" From our studies on rat liver and ascites tumor nuclei, evidence has been obtained that ribonucleoprotein (RNP) complexes containing rapidly labeled RNA (HnRNA and presumably mRNA) are part of an RNP-network which in turn appears to be tightly bound to the nuclear envelope (11). Dissolution of this envelope by nonionic detergent doe not release labeled RNA (11). Aaronson and Blobel (1) and Scheer and co-workers (32) have found that similar treatment removes lipids from the nuclear envelope and that such membrane-denudated nuclei retain both their shape and pore complexes. They reported that these nuclear pore complexes are attached to intranuclear structures, particularly to a distinct peripheral layer of ill-defined nuclear material which they have interpreted as equivalent to the fibrous lamina described in a variety of cell types (14,30,33,35). Berezney and Coffey have shown that a residual nuclear structure which preserves the nuclear shape remains after rat liver nuclei are treated with high salt and digested with ribonucle-

The association of transcribed genes with the nuclear matrix ofDrosophilacells during heat shock

“…Previous work has shown that hnRNAs are bound to the nuclear matrix (36)(37)(38)(39). It was possible that genes were associated with the matrix through their association with this bound hnRNA.…”

The effect of estrogen on the concentration of ovalbumin gene sequence in the 2 M NaCl residual fraction of oviduct chromatin

“…It has been shown that the nuclear skeleton, a structure similarly isolated as the nuclear matrix, binds ribonucleoprotein (RNP) complexes which show rapid labeling of the hnRNA [37]. It has also been shown that the DNA-P fraction is enriched in RNA [20].…”

Control of gene expression by steroid hormones

“…The nuclear skeleton appears to support DNA replication (Pardoll et al, 1980 ;Tubo et al, 1985) and transcription (Robinson et al, 1983 ;Ciejek et al, 1983 ; by tightly anchoring DNP. This structure also binds hnRNP (Herman et al, 1978 ;Miller et al, 1978a ;Van Eekelen and Van Venrooij, 1981) and snRNP (Miller et a/., 1978b ;Gallinaro et al, 1983) Rousseau, 1985). RNA is a potent competitor for the binding of receptor-androgen (Liao et al, 1980), -oestrogen (Feldman et al, 1981 ;Chong and Lippman, 1982), and -dexamethasone (Tymoczko et al, 1982) (Palmiter and Carey, 1974 ;Cox, 1977) ; similarly, oestrogen or progesterone was demonstrated to affect the half-life of coinalbumin mRNA in chick oviduct (Mc Knight and Palmiter, 1979), and androgen to modulate the half-life of prostatic binding protein mRNAs (Page and Parker, 1982).…”