RNA secondary structure repression of a muscle-specific exon in HeLa cell nuclear extracts

The chicken beta-tropomyosin pre-messenger RNA (pre-mRNA) is spliced in a tissue-specific manner to yield messenger RNA's (mRNA's) coding for different isoforms of this protein. Exons 6A and 6B are spliced in a mutually exclusive manner; exon 6B was included in skeletal muscle, whereas exon 6A was preferred in all other tissues. The distal portion of the intron upstream of exon 6B was shown to form stable double-stranded regions with part of the intron downstream of exon 6B and with sequences in exon 6B. This structure repressed splicing of exon 6B to exon 7 in a HeLa cell extract. Derepression of splicing occurred on disruption of this structure and repression followed when the structure was re-formed, even if the structure was formed between two different RNA molecules. Repression leads to inhibition of formation of spliceosomes. Disrupting either of the two double-stranded regions could lead to derepression, whereas re-forming the helices by suppressor mutations reestablished repression. These results support a simple model of tissue-specific splicing in this region of the pre-mRNA.     

A replication cycle for viroids and other small infectious RNA's

Experimental data concerning viroid-specific nucleic acids accumulating in tomato plants establish, together with earlier studies, the major features of a replication cycle for viroid RNA in plant cells. Many features of this pathway, which involves multimeric strands of both polarities, may be shared by other small infectious RNA's including certain satellite RNA's and "virusoid" RNA's which replicate in conjunction with conventional plant viruses. The presence, in host plans, of an elaborate machinery for replicating these disease agents suggests a role for endogenous small RNA's in cellular development.     

Differential control of U1 small nuclear RNA expression during mouse development

During normal mouse development the relative amounts of two types of U1 small nuclear RNA's (U1 RNA) change significantly. Fetal tissues have comparable levels of the two major types of mouse U1 RNA's, mU1a and mU1b, whereas most differentiated adult tissues contain only mU1a RNA's. Those adult tissues that also accumulate detectable amounts of embryonic (mU1b) RNA's (for example, testis, spleen, and thymus) contain a significant proportion of stem cells capable of further differentiation. Several strains of mice express minor sequence variants of U1 RNA's that are subject to the same developmental controls as the major types of adult and embryonic U1 RNA. The differential accumulation of embryonic U1 RNA's may influence the pattern of gene expression during early development and differentiation.     

Two novel classes of small ribonucleoproteins detected by antibodies associated with lupus erythematosus

The RNP and Sm antigens recognized by lupus erythematosus antibodies are located on discrete particles containing single small nuclear RNA's complexed with proteins. The antigens Ro and La are also on ribonucleoproteins. The small RNA's in ribonucleoproteins with Ro are discrete, like those associated with RNP and Sm; in contrast, ribonucleoproteins with La contain a striking highly banded spectrum of small RNA's from uninfected cells as well as virus-associated RNA from adenovirus-infected cells.     

Reading frame selection and transfer RNA anticodon loop stacking

Messenger RNA's are translated in successive three-nucleotide steps (a reading frame), therefore decoding must proceed in only one of three possible frames. A molecular model for correct propagation of the frame is presented based on (i) the measured translational properties of transfer RNA's (tRNA's) that contain an extra nucleotide in the anticodon loop and (ii) a straightforward concept about anticodon loop structure. The model explains the high accuracy of reading frame maintenance by normal tRNA's, as well as activities of all characterized frameshift suppressor tRNA's that have altered anticodon loops.     

Sulfur: incorporation into the transfer fraction of soluble ribonucleic acid

When S(35)-labeled soluble RNA from Escherichia coli K 38 is subjected to gel filtration, four fractions of RNA are obtained by elution. Only one RNA fraction, the transfer RNA, contains sulfur, presumably as thionucleotides. Treatment with ribonuclease suggests that the incorporated sulfur is an integral part of the polynucleotide chain; digestion with alkali yields a mixture of products containing sulfur, the major one being eluted in a position similar to uridine diphosphate upon Dowex-l chromatography. Analysis by countercurrent distribution of S(35)-labeledtransfer RNA from E. coli B reveals that the incorporated sulfur is found in many RNA's that accept amino acids, but the possibility remains that not all acceptor RNA's contain sulfur.     

Inhibition of secretion of hepatitis B surface antigen by a related presurface polypeptide

The presurface (preS) proteins of hepatitis B virus are structural components of the viral envelope that may play important roles in virion assembly and infectivity. They are specified by a large open reading frame that includes the coding region for the major surface (S) protein in its 3' half. Translation of the preS proteins initiates upstream from the S region, giving rise to proteins that are composed of the S domain and an additional 163 (preS1) or 55 (preS2) amino acids. Little is known about the biosynthesis and assembly of these proteins. The expression of the S and preS1 proteins was examined by transfecting cultured mammalian cells with viral DNA and injecting synthetic messenger RNA's into Xenopus oocytes. In contrast to the proteins encoded by the S region, the preS1 proteins are not detectably secreted into the culture medium. Furthermore, when the S and preS1 proteins are synthesized together, secretion of the S proteins is specifically and strongly inhibited. The results suggest a unique molecular interaction during secretion of the S and preS proteins that may be important for virus assembly.     

Messenger RNA structure: compatibility of hairpin loops with protein sequence

Examination of the amino acid sequences of human cytochrome c and the alpha-chain variant of human hemoglobin Constant Spring has revealed the possiblity for base-paired hairpin loops in the messenger RNA's for these proteins. A similar analysis of the bacteriophage R17 coat protein suggests an additional unobserved loop in the R17 RNA. If such loops are present in messenger RNA's generally, it would suggest that DNA has more than one stable base-paired conformation.     

Erythrocyte transfer RNA: change during chick development

Radioactive aminoacyl transfer RNA's isolated from erythrocytes in the blood of 4-day-old chick embryos and from reticulocytes of adult chickens were analyzed by chromatography on methylated albumin kieselguhr and freon columns. Embryonic and adult methionyl transfer RNA's showed qualitative and quantitative differences in both chromatographic systems. The patterns for arginyl, seryl, and tyrosyl transfer RNA's in the two cell types were similar, while the leucyl transfer RNA patterns suggested a difference.     

Genetic expression in the developing brain

The adult mouse brain contains complex populations of polyadenylated [poly(A)+] and nonpolyadenylated [poly(A)-] messenger RNA's (mRNA's). These mRNA's are separate sequence populations, similar in complexity, and in combination are equivalent to approximately 150,000 different mRNA sequences, of average length. Essentially all of the "adult" poly(A)+ mRNA's are present in the brain at birth. In contrast, most of the poly(A)- mRNA's are absent. Brain poly(A)- mRNA's begin to appear soon after birth, but the full adult complement is not reached until young adulthood. This suggests that these poly(A)- mRNA's specify proteins required for the biological capabilities of the brain that emerge during the course of postnatal development.     

冀西北坝上地区大蒜播种期研究

为了探讨冀西北坝上地区大蒜适宜的播种期,给当地大蒜高效生产提供理论依据,试验以大蒜品种西八里为试验材料,设置A(3月22日)、B(4月1日)、C(4月11日)3个不同播期,测定了不同播期下大蒜的生育期、植株性状、蒜头性状、蒜薹和蒜头产量等指标。结果表明,播期B和C较播期A的出苗时间分别缩短7 d和11 d;播期B的植株性状、蒜头性状均优于播期A和C,播期B一级蒜的比例最高,较播期A、C分别高出11.0和27.6个百分点;播期B较播期A和C的蒜薹产量分别提高8.41%和40.82%,蒜头产量分别提高10.19%和16.08%。本试验条件下,坝上地区大蒜适宜的播种期为3月底至清明节之间。     

Specific interactions in RNA enzyme-substrate complexes

Analysis of crosslinked complexes of M1 RNA, the catalytic RNA subunit of ribonuclease P from Escherichia coli, and transfer RNA precursor substrates has led to the identification of regions in the enzyme and in the substrate that are in close physical proximity to each other. The nucleotide in M1 RNA, residue C92, which participates in a crosslink with the substrate was deleted and the resulting mutant M1 RNA was shown to cleave substrates lacking the 3' terminal CCAUCA sequence at sites several nucleotides away from the normal site of cleavage. The presence or absence of the 3' terminal CCAUCA sequence in transfer RNA precursor substrates markedly affects the way in which these substrates interact with the catalytic RNA in the enzyme-substrate complex. The contacts between wild-type M1 RNA and its substrate are in a region that resembles part of the transfer RNA "E" (exit) site in 23S ribosomal RNA. These data demonstrate that in RNA's with very different cellular functions, there are domains with similar structural and functional properties and that there is a nucleotide in M1 RNA that affects the site of cleavage by the enzyme.     

At least three human type alpha interferons: structure of alpha 2

The sequence of a human leukocyte-derived complementary DNA (cDNA), Hif-2h, which directs the formation in Escherichia coli of a polypeptide, IFN-alpha 1, with interferon (IFN) activity has been described. A second IFN cDNA, Hif-SN206, which also elicits synthesis of a biologically active IFN, IFN-alpha 2, is described in this article. Whereas IFN-alpha 2 is twice as active on human as on bovine cells, IFN-alpha 1 is 10 to 20 times more active on bovine than on human cells. As deduced from the cDNA's, the messenger RNA's for the two IFN's differ in length and in 20 percent of the nucleotides; the mature IFN polypeptides differ in 17 percent of the amino acids. Both IFN-alpha 1 and IFN-alpha 2 differ from the lymphoblastoid IFN described by others. Therefore, at least three different IFN-alpha genes are expressed in man; studies on genomic DNA reveal the presence of at least eight IFN-related genes.     

Cloning of a gene whose expression is increased in scrapie and in senile plaques in human brain

A complementary DNA library was constructed from messenger RNA's extracted from the brains of mice infected with the scrapie agent. The library was differentially screened with the objectives of finding clones that might be used as markers of infection and finding clones of genes whose increased expression might be correlated with the pathological changes common to scrapie and Alzheimer's disease. A gene was identified whose expression is increased in scrapie. The complementary DNA corresponding to this gene hybridized preferentially and focally to cells in the brains of scrapie-infected animals. The cloned DNA also hybridized to the neuritic plaques found with increased frequency in brains of patients with Alzheimer's disease.     

Secondary structure of ribosomal RNA

Infrared spectra were obtained for 16S and for 23S ribosomal RNA's in D(2)O solutions. The percentage of each base in the paired and unpaired regions of the RNA was determined from the spectra. The secondary structures of 16S and 23S ribosomal RNA's (from Escherichia coli) are significantly different from each other and are also different from those of yeast ribosomal RNA, formylmethionyl-transfer RNA, and the anticodon fragment of this transfer RNA.