The poly(adenylic acid) sequence of mouse globin messenger RNA

Cx32 mRNA in rat liver: effects of inflammation on poly(A) tail distribution and mRNA degradation

Previous studies showed that the expression of connexin 32 (Cx32), the polypeptide subunit component of the major hepatic gap junction, is reduced in liver by changes in mRNA stability during bacterial lipopolysaccharide (LPS)-induced inflammation. In this study, we examined the distribution of Cx32 mRNA poly(A) tail lengths during LPS-induced inflammation, because this is considered the first step in the degradation of many mRNAs. During LPS treatment the first detectable change in Cx32 mRNA was a gradual shortening of its poly(A) tail, which reached a final size of approximately 20 nucleotides. However, the poly(A) tail did not disappear entirely before the bulk of Cx32 mRNA was degraded. Treatment with actinomycin D, which blocks the degradation of Cx32 mRNA after LPS administration, resulted in the appearance of a completely deadenylated mRNA, which otherwise could not be detected. On the contrary, treatment with cycloheximide resulted in a decrease in the stability of Cx32 mRNA without an apparent change of the poly(A) tail size. The effect of cycloheximide on Cx32 mRNA stability seems to be due indirectly to the induction of an inflammatory response by this drug. These results suggest that, similar for many mRNAs, shortening of the poly(A) tail is one of the first steps in the degradation of Cx32 mRNA during inflammation.

Poly(A) tail shortening by a mammalian poly(A)-specific 3'-exoribonuclease

3'-Exonucleolytic removal of the poly(A) tail is the first and often rate-limiting step in the decay of many eucaryotic mRNAs. In a cytoplasmic extract from HeLa cells, the poly(A) tail of mRNA was degraded from the 3'-end. In agreement with earlier in vivo observations, prominent decay intermediates differed in length by about 30 nucleotides. The Mg2+-dependent, poly(A)-specific 3'-exoribonuclease responsible for this poly(A) shortening activity was purified from calf thymus. A polypeptide of 74 kDa copurified with the activity. The deadenylating nuclease (DAN) required a free 3'-OH group, released solely 5'-AMP, degraded RNA in a distributive fashion, and preferred poly(A) as a substrate. At low salt concentration, the activity of purified DAN was strongly dependent on spermidine or other, yet unidentified factors. Under these reaction conditions, DAN was also stimulated by the cytoplasmic poly(A)-binding protein I (PAB I). At physiological salt concentration, the stimulatory effect of spermidine was weak and PAB I was inhibitory. At either salt concentration DAN and PAB I reconstituted poly(A) shortening with the same pattern of intermediates seen in cytoplasmic extract. The properties of DAN suggest that the enzyme might be involved in the deadenylation of mRNA in vivo.

Brain non-adenylated mRNAs

Most eukaryotic messenger RNA (mRNA) species contain a 3'-poly(A) tract. The histone mRNAs are a notable exception although a subclass of histone-encoding mRNAs is polyadenylated. A class of mRNAs lacking a poly(A) tail would be expected to be less stable than poly(A)+ mRNAs and might, like the histones, have a half-life that varied in response to changes in the intracellular milieu. Brain mRNA exhibits an unusually high degree of sequence complexity; studies published ten years ago suggested that a large component of this complexity might be present in a poly(A)- mRNA population that was expressed postnatally. The question of the existence of a complex class of poly(A)- brain mRNAs is particularly tantalizing in light of the heterogeneity of brain cells and the possibility that the stability of these poly(A)- mRNAs might vary with changes in synaptic function, changing hormonal stimulation or with other modulations of neuronal function. The mRNA complexity analyses, although intriguing, did not prove the existence of the complex class of poly(A)- brain mRNAs. The observed mRNA complexity could have resulted from a variety of artifacts, discussed in more detail below. Several attempts have been made to clone members of this class of mRNA. This search for specific poly(A)- brain mRNAs has met with only limited success. Changes in mRNA polyadenylation state do occur in brain in response to specific physiologic stimuli; however, both the role of polyadenylation and de-adenylation in specific neuronal activities and the existence and significance of poly(A)- mRNAs in brain remain unclear.

The Role of the poly(A) sequence in mammalian messenger RNA

The poly(A) sequence is added to 3' termini of nuclear RNA segments destined to become part of the mRNA, and may play an essential role in the selection of these segments. It appears to be required for at least some of the splicing events involved in mRNA processing. In the cytoplasm, the poly(A) segment is the target of a degradation process which causes its gradual shortening, and leads to a heterogeneous steady-state poly(A)-size distribution. Complete loss of the poly(A) is probably followed by inactivation of the mRNA, since chains depleted of poly(A) do not accumulate in the cells. A role for this sequence in the promotion of mRNA stability is suggested by the behavior of globin mRNA depleted of poly(A) after injection into frog oocytes. The poly(A) shortening process may be part of the mRNA inactivation mechanism, as indicated by the greater sensitivity to degradation of the poly(A) of some short-lived mRNAs. However, the stochastic mRNA decay implies that new and old mRNA chains, with long and short poly(A) segments, respectively are equally susceptible to inactivation. The poly(A)-lacking histone mRNAs are stable only in cells engaged in DNA replication. Present knowledge favors a role for poly(A) in the control of mRNA stability. Loss of this sequence could be controlled through modulation of poly(A)-protein interactions or through masking of a sequence directly adjacent to the poly(A). In the nucleus, the poly(A) sequence could also serve as stabilizing agent, but, in addition, it might interact with the splicing machinery.

Biochemical characterization of RNA and protein synthesis in erythrocyte development

Newts (Triturus cristatus) made anemic with acetylphenylhydrazine (APH) fail to regenerate erythrocytes (RBC's) immediately and exhibit a latent period of 1.5-2 wk during which animals lack RBC's and are aplastic. With the establishment of erythroid regeneration at 10-14 days, relatively homogeneous populations of successive erythropoietic stages occur in the blood. This feature makes possible biochemical analyses of events in early, intermediate, and late developmental stages, respectively, each of which can be obtained in vivo with minimal contamination by other stages. Previous studies have described a primitive cell population referred to as "erythroid precursor cells" (EPC's) which precedes the appearance of definitive erythroid elements. The present studies show that EPC's and early erythroid cells are engaged mainly in ribosomal production, including synthesis of rRNA and ribosomal proteins. Moreover, EPC's and early erythroid cells also synthesize tRNA and a presumed Hb-mRNA which has been identified by its sedimentation rate at 9-12 s and its content of polyadenylic acid. In intermediate stages, there occurs a fourfold decrease in the level of RNA synthesis and, while rRNA continues to be formed, there is a disproportionate accumulation of the two major cytoplasmic rRNA species in favor of the large ribosomal subunit RNA. In late developmental stages, the level of RNA synthesis is markedly diminished with little or no evidence of formation of defined RNA classes. Correlated radioautographic and biochemical studies with radioactive delta-aminolevulinic acid and leucine indicate that EPC's and other early erythroid elements synthesize not only hemoglobin but also ferritin and ribosomal proteins. It is concluded that: (a) erythroid RNA synthesis is most pronounced in the early developmental stages, being manifested predominantly by rRNA production but including tRNA and Hb-mRNA; (b) intermediate developmental stages show both "ribosomal wastage" and decreased growth rate, marking a pivotal point between the transcriptional activities of early stages and translational activities of late stages; (c) EPC's represent a cell population already committed to RBC formation and are excluded from a role as the pluripotential stem cell.

The polyadenylic sequences in the ribonucleic acid of the fern Anemia phyllitidis

The vegetative prothalli (1-3 weeks old) of Anemia were incubated for 24 h in [(14)C]adenine. The RNA was phenol extracted from whole cells and the poly (A) sequences were isolated by nuclease digestion followed by poly (U)-sepharose chromatography. About 2-3% of the total radioactivity was retained on the column. The base composition of the nuclease resistant RNA was: C, 1.4; G, 3.6; A, 93.3; and U, 1.7. It is concluded that Anemia RNA contains poly adenylate sequences.

Modified nucleosides and 5'-end groups in purified mouse immunoglobulin light chain mRNA and rabbit globin mRNA detected by borohydride labelling

The borohydride reaction has been used to investigate modified nucleosides and end groups in purified immunoglobulin light chain mRNA and rabbit globin mRNA. 1. The light chain mRNA was isolated from the microsomal fraction of MOPC 41A mouse myelomas, which secrete kappa chains, by two cycles of oligo(dT) cellulose chromatography and glycerol gradient centrifugation. The 12 S mRNA was active in a Krebs II ascites cell-free system and appeared to be homogenous as judged by gradient centrifugation, polyacrylamide gel electrophoresis in 98% formamide and fingerprint analysis of 125I-labelled mRNA. 2. End group labelling of the light chain and globin mRNAs by oxidation with periodate and reduction with boro[3H]hydride showed that the RNAs have a 5'-terminal 7-methyl guanosine in 5'-pyrophosphate linkage with the next nucleoside. 3. To detect any modified residues in the interior of chains, nucleosides in complete digests of the mRNAs were converted by the borohydride reaction to 3H-labelled nucleoside trialcohols, which were fractionated by two dimensional chromatography (the Randerath technique). The light chain mRNA was found to contain N6-methyl adenosine (1 mole) but the rabbit globin mRNAs lacked this nucleoside. Deficiencies in this technique for analysis of minor constituents in large RNAs were noted.

Globin messenger RNA from anaemic rabbit spleen. Size of its polyadenylate segment

The size of the polyadenylate segment of globin messenger RNA isolated from spleens of anaemic rabbits was estimated by comparison of its electrophoretic migration in polyacrylamide gels to that of synthetic poly(A) segments of known lengths. Conditions of enzymic degradation of mRNA with pancreatic ribonuclease and T1 ribonuclease were carefully established in order to ensure complete degradation of the heteropolymeric part of mRNA without affecting the polyadenylate sequence. The poly (A) segments of spleen globin mRNA were found to be 25-90 nucleotides long whilst those of peripheral blood reticulocytes from the same animals were only 10-30 residues long. Since spleen contains young erythroid cells and since anucleated blood reticulocytes constitute a statistically older population of the same cell line, these results support the idea that the poly(A) segment of mRNA shortens when the message ages.

The nature of the 5'-linked 5' nucleotide sequence at the 5' end of rabbit globin messenger ribonucleic acid

Poly(A)-containing messenger RNA isolated from rabbit reticulocytes as estimated by periodate oxidation and condensation with [3H]isoniazid has two oxidizable end groups per molecule of mol. wt. 220000. When the mRNA is subjected to stepwise degradation by beta-elimination, only one oxidizable end-group is found. This indicates that one of the 2',3' hydroxyl end-groups is linked through the normal 3'--5' phosphodiester bond, but that the other is linked in such a way that after stepwise degradation no new 2',3 hydroxyl group is revealed. This structure could be a 5'-linked 5'-phospho di- or tri-ester. On digestion with ribonuclease the isoniazid-labelled RNA produced oligonucleotide hydrazones consistent with a poly(A) sequence at the 3' end plus fragments that are not found after stepwise degradation. These fragments have a charge of --6 and --8 from pancreatic ribonuclease or --7 from ribonuclease T1 digestion. These charges are changed to --3.4 and --4.1 after pancreatic ribonuclease, ribonuclease T2 and alkaline phosphatase digestion. methyl-3H-labelled-poly(A)-containing RNA isolated from late erythroid cells contain a methyl-labelled fragment resistant to endonuclease and phosphodiesterase II digestion. After digestion with phosphodiesterase I this fragment produces methyl-3 H-labelled nucleotides with the electrophoretic mobility of pm7G and pAm. It is concluded that globin mRNA has the 5' sequences m7G(5')ppp'AmpYpGp ... and m7G(5')pppAmpApGpYp.

Molecular modifications associated with Aging of globin messenger RNA in vitro

Using polyacrylamide gel elution-electrophoresis in aqueous medium, highly purified rabbit globin mRNA can be fractionated into several populations of molecules differing by their mean poly(A) content. Both alpha and beta globin mRNA are heterogenous with respect to their electrophoretic mobilities. With the conditions used no separation of alpha and beta globin mRNA occurs during electrophoresis. From the specific radioactivity distribution in the different mRNA fractions one can conclude that the polyadenylate sequence at the 3' end of globin mRNA molecules becomes shorter with aging. This shortening occurs on alpha as well as beta, globin mRNAs and the extent of heterogeneity in poly(A) content is similar for both globin mRNAs. Furthermore, using two different methods of mRNA fractionation (polyacrylamide gel elution-electrophoresis and elution of poly (U)-Sepharose-bound mRNA at increasing temperatures) it is shown that old mRNA molecules differ from relatively young messages in their ability to direct cell-free globin synthesis. Modifications reducing template activity in vitro thus seem to take place during globin mRNA aging.

The enzymic addition of poly(A) to the 3'-end of RNA using bacteriophage MS 2 RNA as a model system

ATP : RNA adenyltransferase, purified from Escherichia coli, was used to add a series of adenosine residues to the 3'-end of MS2RNA. Incubations of the order of a few minutes at 37 degrees C were sufficient for synthesis of a short poly(A) chain that did not appreciably alter the hydrodynamic or electrophoretic properties of MS2 RNA. The size of the poly(A) tails was estimated by gel electrophoresis after prior hydrolysis of the primer RNA with pancreatic ribonuclease. These results were in good agreement with the values calculated on the basis of the relative amount of incorporated AMP. After the addition of a short poly(A) tail, approximately 50% of the treated material binds specifically to an oligo(dT)-cellulose column. The majority of the recovered poly(a)-containing RNA was still intact, as shown by analysis on polyacrylamide gel. After incubations beyond 6 min, slowly sedimenting material, also showing reduced electrophoretic mobility, was formed. Presumably this material corresponds to RNA chains to which long poly(A) tails are linked.

Nucleotide sequences of the 3'-terminal untranslated region of messenger RNA for human beta globin chain

In normal messenger RNA for the human beta-globin chain, nucleotide sequences have been identified which can be matched to the amino-acid sequence of the abnormally long segment of the beta-chain of hemoglobin Cranston. The finding of these sequences strengthens the hypothesis that the betaCranston chain arose by a frameshift mutation allowing the "readthrough" of the normal termination codon and translation of usually untranslated portions of the messenger RNA for the beta-globin chain. The oligonucleotides which match the amino-acid sequence of hemoglobin Cranston provide a sequence of 36 nucleotides which follows the normal beta-chain termination codon UAA.

A kinetic estimation of base sequence complexity of nuclear poly(A)-containing RNA in mouse Friend cells

Complementary DNA (cDNA) has been transcribed by viral reverse transcriptase from poly(A)-containing nuclear RNA prepared from growing mouse Friend cells (clone M2). Annealing experiments with this cDNA have demonstrated that a large proportion of the poly(A) tracts in M2 cell nuclear RNA are adjacent to RNA sequences which are transcribed from nonrepetitive DNA in the mouse genome. The kinetics of hybridization of cDNA to template RNA indicate that nuclear poly(A)-containing RNA consists of at least two abundance classes, the more complex of which is transcribed from approximately 3 percent of the genome. Thus there are at least 5 times more unique DNA sequences represented in nuclear polyadenylated RNA than in polysomal polyadenylated RNA. Moreover, there is evidence for posttranscriptional mechanisms which alter the relative concentrations of some (at least) gene transcripts between nucleus and cytoplasm.

The polyA regions of hen oviduct RNA

Total RNA from hen oviduct has been hydrolysed with a mixture of T(1) and pancreatic ribonucleases. Poly(A) tracts in the digestion product have been isolated by binding to oligo(dT) cellulose. Of the four major ribonucleotides, the product has been shown to contain only adenylic acid. When separated on polyacrylamide gels, the poly(A) gave two peaks corresponding to average apparent lengths of 270-280 and 540-550 nucleotides.