Some aspects of double-stranded hairpin structures in heterogeneous nuclear RNA

The effect of inhibition of RNA synthesis by actinomycin D on the population of basic polypeptides of the 30S unclear ribonucleoprotein particles

In rats injected intraperitoneally with actinomycin D (2 mg/kg body weight) 12 h earlier, the yield of the 30S ribonucleoprotein particles isolated from liver nuclei by extraction with 0.1 M NaCl at pH 8.0 decreased by 60 per cent. The protein-to-RNA ratio of these particles increased to 32:1 from the ratio 4.4:1 found in the same particles isolated from the nuclei of liver of control rats. The particles isolated from the liver nuclei of rats injected with actinomycin D were depleted of all charge isomers of the two most prominent polypeptides (33,000 and 39,000 daltons) present in the particles of liver of control animals. The most abundant protein in these particles was a 43,000 dalton polypeptide. This polypeptide is the least prominent of the 3 major polypeptides present in the control particles. The same charge isomers of the 43,000 dalton polypeptide were present in the nuclear ribonucleoprotein particles isolated from the liver of control animals and from the liver of animals treated with actinomycin D 12 h earlier. In control animals the nuclear ribonucleoprotein monoparticles isolated from kidney contained 3 major polypeptides of the same molecular weight with the same distribution of their charge isomers as were present in the particles isolated from liver nuclei. The injection of actinomycin D 12 h earlier was without any effect on the protein composition of the 30S nuclear ribonucleoprotein particles of rat kidney.

Nucleotide sequence complementarity between adenovirus 2-coded VA RNA and host cell pre-mRNA. A possible regulatory mechanism of cellular RNA splicing by VA RNA

Using a computer program, complementary of nucleotide sequences was assessed between adenovirus 2-coded VA RNA and presumptive cellular and viral 'pre-mRNAs'. In this paper, the possibility is considered that the splicing of cellular 'pre-mRNA' can be regulated in such a way that the formation of the proper intramolecular double-stranded hairpin structures, key elements for RNA splicing, is prevented by the binding of VA RNAI or RNAII to the nucleotide sequences around the exon-intron and intron-exon joint sites of cellular 'pre-mRNA' molecules. Complementarity assessment showed that VA RNAI can bind to the joint sites in such a way as to form an omega shape at two separate regions around the joint sites of cellular 'pre-mRNA'. Whereas VA RNAI is not capable of binding to viral hexon 'pre-mRNA' in the same manner as it does to cellular 'pre-mRNA', the binding may occur in a different way. Such differential binding is discussed in relation to the post-transcriptional sequence selection which takes place during the late phase of adenovirus infection.

A possible regulatory mechanism in RNA processing and its implication for posttranscriptional sequence control during differentiation of cell function

1. This paper is concerned with the possible molecular mechanism for RNA processing including posttranscriptional sequence control underlying the differentiation of cell functions. 2. It was previously postulated that intramolecular double-stranded hairpin structures present at 5'- and 3'-terminal regions of a 'pre-mRNA' are key elements for RNA splicing [24]. 3. In this paper the possibility is considered that the splicing of 'pre-mRNA' can be regulated in such a way that the formation of the proper double-stranded hairpin structures is prevented by the binding of low-molecular-weight nuclear RNA (LnRNA) to the terminal regions and/or to the nucleotide sequences around the exon-intron and intron-exon joint sites of the 'pre-mRNA' molecules. 4. Complementarity assessment of nucleotide sequences of rat preproinsulin 'pre-mRNA' and rat LnRNA, i.e. Ul, showed that Ul RNA is capable of forming stable double-standard intermolecular structures around the joint sites of preproinsulin 'pre-mRNA' and may prevent the formation of intramolecular double-stranded structures required for RNA splicing. This may imply a regulatory (inhibitory) role for Ul RNA in the processing of 'pre-mRNA'. 5. A possible regulatory role of LnRNA in RNA splicing is discussed in relation to the determination of the mRNA population to be translated in the cytoplasm during differentiation of cell functions.

Electron microscopic observations of heterogeneous nuclear RNA of chicken reticulocytes

Secondary structures of annealed, snapped-back and untreated chicken reticulocyte poly(A)-containing nuclear RNA were investigated by electron microscopy. Three shapes of molecules were observed: 'coat'hanger' shaped, loop-bearing and filamentous molecules. The former two shaped molecules consist of a small and large fold-back or loop plus a short hook or tail, corresponding to the poly(A) segment at the apparent middle of the structure. The third shaped molecule, mainly seen after snap-back treatment, possesses a small fold-back structure at one end only. It is suggested that the small and large fold-backs or loops of the molecule represent the 5'- and 3'-terminal hairpin structures, respectively. Two distinct sizes of molecule, small and large, irrespective of molecule shape, were observed.

Ribonucleoprotein structure in nascent hnRNA is nonrandom and sequence-dependent

We have studied the ribonucleoprotein morphology of nascent hnRNA using chromatin spreading methods. This approach allows visualization of multiple transcripts of the same DNA sequence. Thus the RNP structure of hnRNA molecules with the same nucleotide sequence can be compared. We find that RNP particles averaging 240 A in diameter occur on the majority of hnRNA transcription units, but that RNA fibrils are generally not completely covered with particles. Furthermore, the RNP particle location is nonrandom for the transcripts of a given gene. Particle number and arrangement on RNP fibrils vary from one transcription unit to the next, and are not obviously related to transcription unit size or activity. Analysis of particle location with respect to the 5' RNA terminus allows RNP particle localization to homologous sequences of less than 500 ribonucleotides on the different fibrils of a single transcription unit. RNP particles assemble very soon after synthesis of the particular sequence. Sites of particle formation are distinct from sites of double-stranded hairpin loops on the RNA fibrils. A differential, or differentially stable, RNP structure with respect to RNA sequence may bear on mechanisms of specific hnRNA processing.

Complete nucleotide sequence of a cloned chicken alpha-globin cDNA

Chicken globin double-stranded cDNA was synthesised from anaemic adult reticulocyte alpha- and beta-globin mRNA and ligated into the Hind III site of pBR322 using synthetic Hind III decamers. Transformation of E. coli x1776 resulted in the production of a number of alpha- and beta-cDNA clones. One of the alpha-type clones (pCG alpha-8) was fully sequenced and found to code for neither alpha A- nor alpha D-globin. Partial sequencing of the other alpha-cDNA clones indicates that they are all of the same type.