Newly formed mRNA lacking polyadenylic acid enters the cytoplasm and the polyribosomes but has a shorter half-life in the absence of polyadenylic acid

The effects of aging on biosynthetic processes in the rat hypothalamic osmoregulatory neuroendocrine system

Elderly people exhibit a diminished capacity to cope with osmotic challenges such as dehydration. We have undertaken a detailed molecular analysis of arginine vasopressin (AVP) biosynthetic processes in the supraoptic nucleus (SON) of the hypothalamus and secretory activity in the posterior pituitary of adult (3 months) and aged (18 months) rats, to provide a comprehensive analysis of age-associated changes to the AVP system. By matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis, we identified differences in pituitary peptides, including AVP, in adult and aged rats under both basal and dehydrated states. In the SON, increased Avp gene transcription, coincided with reduced Avp promoter methylation in aged rats. Based on transcriptome data, we have previously characterized a number of novel dehydration-induced regulatory factors involved in the response of the SON to osmotic cues. We found that some of these increase in expression with age, while dehydration-induced expression of these genes in the SON was attenuated in aged rats. In summary, we show that aging alters the rat AVP system at the genome, transcriptome, and peptidome levels. These alterations however did not affect circulating levels of AVP in basal or dehydrated states.

Inactivation of SSM4, a new Saccharomyces cerevisiae gene, suppresses mRNA instability due to rna14 mutations

Decay rates of mRNAs depend on many elements and among these, the role of the poly(A) tail is now well established. In the yeast Saccharomyces cerevisiae, thermosensitive mutations in two genes, RNA14 and RNA15, result in mRNAs having shorter poly(A) tails and reduced half-life. To identify other components interacting in the same process, we have used a genetic approach to isolate mutations that suppress the thermosensitivity of an rna14 mutant strain. Mutations in a single locus, named SSM4, not only suppress the cell growth phenotype but also the mRNA instability and extend the short mRNA poly(A) tails. The frequency of appearance and the recessive nature of these mutations suggested that the suppressor effect was probably due to a loss of function. We failed to clone the SSM4 gene directly by complementation, owing to its absence from gene banks; it later emerged that the gene is toxic to Escherichia coli, but we have nevertheless been able to clone the SSM4 sequence by Ty element transposition tagging. Disruption of the SSM4 gene does not affect cell viability and suppresses the rna14 mutant phenotypes. The protein encoded by the SSM4 gene has a calculated molecular mass of 151 kDa and does not contain any known motif or show homology with known proteins. The toxicity of the SSM4 gene in E. coli suggests that a direct biochemical activity is associated with the corresponding protein.

Synthesis of oxytocin in amnion, chorion, and decidua may influence the timing of human parturition

Despite the widespread clinical use of oxytocin (OT) as a potent and specific stimulant of labor, previous research data have not supported a role for OT in the physiology of normal human parturition. We have demonstrated synthesis of OT mRNA in amnion, chorion, and decidua using Northern blot analysis, ribonuclease protection assays, and in situ hybridization. Probes directed towards both the 3' and 5' ends of the gene have been used. Levels were highest in decidua with considerably less in chorion and amnion and very low levels in placenta. The transcript size in decidua appears to be 60-80 nucleotides smaller than the transcripts in amnion and chorion. OT gene expression in chorio-decidual tissues increased three- to fourfold around the time of labor onset. Estradiol stimulated synthesis of OT mRNA during in vitro incubation. These results support the hypothesis of a paracrine system involving OT and sex steroids within intrauterine tissues wherein significant changes could occur without being reflected in the maternal circulation. Such a paracrine system could rationalize a long-sought role for oxytocin in the physiology of human labor. These data may lead to novel approaches towards prevention or treatment or preterm labor.

Mutations in the yeast RNA14 and RNA15 genes result in an abnormal mRNA decay rate; sequence analysis reveals an RNA-binding domain in the RNA15 protein

In Saccharomyces cerevisiae, temperature-sensitive mutations in the genes RNA14 and RNA15 correlate with a reduction of mRNA stability and poly(A) tail length. Although mRNA transcription is not abolished in these mutants, the transcripts are rapidly deadenylated as in a strain carrying an RNA polymerase B(II) temperature-sensitive mutation. This suggests that the primary defect could be in the control of the poly(A) status of the mRNAs and that the fast decay rate may be due to the loss of this control. By complementation of their temperature-sensitive phenotype, we have cloned the wild-type genes. They are essential for cell viability and are unique in the haploid genome. The RNA14 gene, located on chromosome H, is transcribed as three mRNAs, one major and two minor, which are 2.2, 1.5, and 1.1 kb in length. The RNA15 gene gives rise to a single 1.2-kb transcript and maps to chromosome XVI. Sequence analysis indicates that RNA14 encodes a 636-amino-acid protein with a calculated molecular weight of 75,295. No homology was found between RNA14 and RNA15 or between RNA14 and other proteins contained in data banks. The RNA15 DNA sequence predicts a protein of 296 amino acids with a molecular weight of 32,770. Sequence comparison reveals an N-terminal putative RNA-binding domain in the RNA15-encoded protein, followed by a glutamine and asparagine stretch similar to the opa sequences. Both RNA14 and RNA15 wild-type genes, when cloned on a multicopy plasmid, are able to suppress the temperature-sensitive phenotype of strains bearing either the rna14 or the rna15 mutation, suggesting that the encoded proteins could interact with each other.

Mutations in the yeast RNA14 and RNA15 genes result in an abnormal mRNA decay rate; sequence analysis reveals an RNA-binding domain in the RNA15 protein

In Saccharomyces cerevisiae, temperature-sensitive mutations in the genes RNA14 and RNA15 correlate with a reduction of mRNA stability and poly(A) tail length. Although mRNA transcription is not abolished in these mutants, the transcripts are rapidly deadenylated as in a strain carrying an RNA polymerase B(II) temperature-sensitive mutation. This suggests that the primary defect could be in the control of the poly(A) status of the mRNAs and that the fast decay rate may be due to the loss of this control. By complementation of their temperature-sensitive phenotype, we have cloned the wild-type genes. They are essential for cell viability and are unique in the haploid genome. The RNA14 gene, located on chromosome H, is transcribed as three mRNAs, one major and two minor, which are 2.2, 1.5, and 1.1 kb in length. The RNA15 gene gives rise to a single 1.2-kb transcript and maps to chromosome XVI. Sequence analysis indicates that RNA14 encodes a 636-amino-acid protein with a calculated molecular weight of 75,295. No homology was found between RNA14 and RNA15 or between RNA14 and other proteins contained in data banks. The RNA15 DNA sequence predicts a protein of 296 amino acids with a molecular weight of 32,770. Sequence comparison reveals an N-terminal putative RNA-binding domain in the RNA15-encoded protein, followed by a glutamine and asparagine stretch similar to the opa sequences. Both RNA14 and RNA15 wild-type genes, when cloned on a multicopy plasmid, are able to suppress the temperature-sensitive phenotype of strains bearing either the rna14 or the rna15 mutation, suggesting that the encoded proteins could interact with each other.

Discordant expression of the immediate-early 1 and 2 gene regions of human cytomegalovirus at early times after infection involves posttranscriptional processing events

Expression of the immediate-early 1 and 2 (IE-1 and IE-2) gene region of human cytomegalovirus (HCMV) was studied during initial phases of the replicative cycle. Accumulation of RNA from IE-1 and -2 was found to be differential. Transcripts from IE-2 reached peak levels very early in infection between 3 and 5 h, whereas IE-1 RNA peak levels were detected later, between 6 and 8 h. A strong decrease in steady-state levels of a 2.2-kb IE-2 RNA was observed at a time when IE-1 transcripts showed a further increase in abundance. Northern (RNA) blot experiments revealed that expression of both the IE-1 RNA and the 2.2-kb IE-2 transcript is controlled by the IE-1 enhancer-promoter. Nuclear run-on experiments demonstrated equal rates of primary transcription for IE-1 and -2 at a time when different steady-state levels of RNA were observed. Concomitant with down-regulation of IE-2 RNAs, a decrease in the size of the IE-1 transcript was detected. At 2 to 5 h after infection the IE-1 transcript migrated at 1.95 kb, whereas later in the replicative cycle the RNA was found at 1.8 kb. RNase H blot analysis revealed that this size discrepancy is due to a shorter poly(A) tail of the IE-1 RNA at early times after infection. These experiments suggest that in addition to transcriptional regulation, specific posttranscriptional mechanisms are involved in controlling expression from the IE-1 and -2 gene region of HCMV.

Poly(A) tail shortening is the translation-dependent step in c-myc mRNA degradation

The highly unstable c-myc mRNA has been shown to be stabilized in cells treated with protein synthesis inhibitors. We have studied this phenomenon in an effort to gain more insight into the degradation pathway of this mRNA. Our results indicate that the stabilization of c-myc mRNA in the absence of translation can be fully explained by the inhibition of translation-dependent poly(A) tail shortening. This view is based on the following observations. First, the normally rapid shortening of the c-myc poly(A) tail was slowed down by a translation block. Second, c-myc messengers which carry a short poly(A) tail, as a result of prolonged actinomycin D or 3'-deoxyadenosine treatment, were not stabilized by the inhibition of translation. We propose that c-myc mRNA degradation proceeds in at least two steps. The first step is the shortening of long poly(A) tails. This step requires ongoing translation and thus is responsible for the delay in mRNA degradation observed in the presence of protein synthesis inhibitors. The second step involves rapid degradation of the body of the mRNA, possibly preceded by the removal of the short remainder of the poly(A) tail. This last step is independent of translation.

Poly(A) tail shortening is the translation-dependent step in c-myc mRNA degradation

The highly unstable c-myc mRNA has been shown to be stabilized in cells treated with protein synthesis inhibitors. We have studied this phenomenon in an effort to gain more insight into the degradation pathway of this mRNA. Our results indicate that the stabilization of c-myc mRNA in the absence of translation can be fully explained by the inhibition of translation-dependent poly(A) tail shortening. This view is based on the following observations. First, the normally rapid shortening of the c-myc poly(A) tail was slowed down by a translation block. Second, c-myc messengers which carry a short poly(A) tail, as a result of prolonged actinomycin D or 3'-deoxyadenosine treatment, were not stabilized by the inhibition of translation. We propose that c-myc mRNA degradation proceeds in at least two steps. The first step is the shortening of long poly(A) tails. This step requires ongoing translation and thus is responsible for the delay in mRNA degradation observed in the presence of protein synthesis inhibitors. The second step involves rapid degradation of the body of the mRNA, possibly preceded by the removal of the short remainder of the poly(A) tail. This last step is independent of translation.

Heterogeneity of human serum amyloid A protein. Five different variants from one individual demonstrated by cDNA sequence analysis

Serum amyloid A (SAA), a chemically polymorphic protein, is the most sensitive marker protein of the acute phase and the precursor of reactive amyloidosis, which is characterized by deposits of amyloid A protein (AA). We investigated the variability of the SAA gene family in one individual by sequencing 11 SAA-specific clones from an acute-phase-liver cDNA library. At least five different SAA variants were deduced from six different cDNAs. The 3' untranslated gene segments fall into two groups, based on nucleotide sequence and variability in length. Various nucleotide and amino acid substitutions were found predominantly in the 3' portion. Some of these substitutions are unique and increase the number of SAA variants in one individual to at least five. Moreover, genomic DNA of four individuals was examined by analysis of restriction-fragment length polymorphism. Besides two conserved strongly labelled bands, additional polymorphic bands were observed, indicating isotypic and/or allotypic SAA variations. Finally, three different mRNA species were detected by Northern-blot analysis, a finding that might be of relevance for the stability of SAA transcripts.

3' noncoding region of phosphoenolpyruvate carboxykinase mRNA contains a glucocorticoid-responsive mRNA-stabilizing element

The stabilization of phosphoenolpyruvate carboxykinase mRNA by glucocorticoids appears to result from the interaction of an induced factor with an RNA element located in the 3' noncoding sequence of the mRNA. This element can confer glucocorticoid-dependent stabilization upon a heterologous mRNA, and thus strategies developed to investigate the control of mRNA transcription can now be applied to the analysis of hormone-regulated mRNA stabilization.

Transcriptional and posttranscriptional regulation contributes to the sex-regulated expression of two sequence-related genes at the janus locus of Drosophila melanogaster

We investigated the structure and developmental pattern of expression of two genes clustered at the janus locus, located at 99D.3R. Data obtained from genomic and cDNA sequencing and from a combination of S1 mapping and primer extension experiments indicated a very unusual organization of this locus, which appeared to be composed of two partially overlapping genes, designated janA and janB. These two genes were found to be transcribed in the same direction. janA encoded one minor and two major transcripts. The 5' end of the janB mRNA mapped within the 3' untranslated region of the janA transcribed sequence. The overlapping region was 118 bases long. Similarities observed between these two genes with respect to both peptidic sequence and intron position strongly suggested that this locus originated from the duplication of an ancestral transcription unit. However, each of the resulting genes has acquired its own specificity of expression linked to sex determination. The janB transcript was detected only in males, and its expression at the adult stage was restricted to germ line cells. The janA gene displayed a much more complex expression; one of the major mRNAs was found in both sexes and at all stages, whereas the two other janA transcripts were expressed only in males.

Expression of the poly(A)-binding protein during development of Xenopus laevis

We have isolated and sequenced cDNA clones encoding the poly(A)-binding protein of Xenopus laevis oocytes. Polyclonal antiserum was raised against a fusion protein encoding 185 amino acids of the Xenopus poly(A)-binding protein. This antiserum localizes the poly(A)-binding protein to subcellular sites associated with protein synthesis; in the retina, immunoreactive protein is detected in the synthetically active inner segment of the photoreceptor but not in the transductive outer segment. Transcripts encoding the poly(A)-binding protein are present in oocytes, although no protein is detected on protein blots. In contrast, the levels of both transcripts and protein increase in development, which correlates with the observed increase in total poly(A) during Xenopus embryogenesis (N. Sagata, K. Shiokawa, and K. Yamana, Dev. Biol. 77:431-448, 1980).

Transcriptional and posttranscriptional regulation contributes to the sex-regulated expression of two sequence-related genes at the janus locus of Drosophila melanogaster

We investigated the structure and developmental pattern of expression of two genes clustered at the janus locus, located at 99D.3R. Data obtained from genomic and cDNA sequencing and from a combination of S1 mapping and primer extension experiments indicated a very unusual organization of this locus, which appeared to be composed of two partially overlapping genes, designated janA and janB. These two genes were found to be transcribed in the same direction. janA encoded one minor and two major transcripts. The 5' end of the janB mRNA mapped within the 3' untranslated region of the janA transcribed sequence. The overlapping region was 118 bases long. Similarities observed between these two genes with respect to both peptidic sequence and intron position strongly suggested that this locus originated from the duplication of an ancestral transcription unit. However, each of the resulting genes has acquired its own specificity of expression linked to sex determination. The janB transcript was detected only in males, and its expression at the adult stage was restricted to germ line cells. The janA gene displayed a much more complex expression; one of the major mRNAs was found in both sexes and at all stages, whereas the two other janA transcripts were expressed only in males.

Expression of the poly(A)-binding protein during development of Xenopus laevis

We have isolated and sequenced cDNA clones encoding the poly(A)-binding protein of Xenopus laevis oocytes. Polyclonal antiserum was raised against a fusion protein encoding 185 amino acids of the Xenopus poly(A)-binding protein. This antiserum localizes the poly(A)-binding protein to subcellular sites associated with protein synthesis; in the retina, immunoreactive protein is detected in the synthetically active inner segment of the photoreceptor but not in the transductive outer segment. Transcripts encoding the poly(A)-binding protein are present in oocytes, although no protein is detected on protein blots. In contrast, the levels of both transcripts and protein increase in development, which correlates with the observed increase in total poly(A) during Xenopus embryogenesis (N. Sagata, K. Shiokawa, and K. Yamana, Dev. Biol. 77:431-448, 1980).

The poly(A)-poly(A)-binding protein complex is a major determinant of mRNA stability in vitro

Using an in vitro mRNA decay system, we investigated how poly(A) and its associated poly(A)-binding protein (PABP) affect mRNA stability. Cell extracts used in the decay reactions were depleted of functional PABP either by adding excess poly(A) competitor or by passing the extracts over a poly(A)-Sepharose column. Polyadenylated mRNAs for beta-globin, chloramphenicol acetyltransferase, and simian virus 40 virion proteins were degraded 3 to 10 times faster in reactions lacking PABP than in those containing excess PABP. The addition of purified Saccharomyces cerevisiae or human cytoplasmic PABP to PABP-depleted reactions stabilized the polyadenylated mRNAs. In contrast, the decay rates of nonpolyadenylated mRNAs were unaffected by PABP, indicating that both the poly(A) and its binding protein were required for maintaining mRNA stability. A nonspecific single-stranded binding protein from Escherichia coli did not restore stability to polyadenylated mRNA, and the stabilizing effect of PABP was inhibited by anti-PABP antibody. The poly(A) tract was the first mRNA segment to be degraded in PABP-depleted reactions, confirming that the poly(A)-PABP complex was protecting the 3' region from nucleolytic attack. These results indicate that an important function of poly(A), in conjunction with its binding protein, is to protect polyadenylated mRNAs from indiscriminate destruction by cellular nucleases. A model is proposed to explain how the stability of an mRNA could be affected by the stability of its poly(A)-PABP complex.

The poly(A)-poly(A)-binding protein complex is a major determinant of mRNA stability in vitro

Using an in vitro mRNA decay system, we investigated how poly(A) and its associated poly(A)-binding protein (PABP) affect mRNA stability. Cell extracts used in the decay reactions were depleted of functional PABP either by adding excess poly(A) competitor or by passing the extracts over a poly(A)-Sepharose column. Polyadenylated mRNAs for beta-globin, chloramphenicol acetyltransferase, and simian virus 40 virion proteins were degraded 3 to 10 times faster in reactions lacking PABP than in those containing excess PABP. The addition of purified Saccharomyces cerevisiae or human cytoplasmic PABP to PABP-depleted reactions stabilized the polyadenylated mRNAs. In contrast, the decay rates of nonpolyadenylated mRNAs were unaffected by PABP, indicating that both the poly(A) and its binding protein were required for maintaining mRNA stability. A nonspecific single-stranded binding protein from Escherichia coli did not restore stability to polyadenylated mRNA, and the stabilizing effect of PABP was inhibited by anti-PABP antibody. The poly(A) tract was the first mRNA segment to be degraded in PABP-depleted reactions, confirming that the poly(A)-PABP complex was protecting the 3' region from nucleolytic attack. These results indicate that an important function of poly(A), in conjunction with its binding protein, is to protect polyadenylated mRNAs from indiscriminate destruction by cellular nucleases. A model is proposed to explain how the stability of an mRNA could be affected by the stability of its poly(A)-PABP complex.

The vasopressin mRNA poly(A) tract is unusually long and increases during stimulation of vasopressin gene expression in vivo

We developed a method, termed an H-blot, by which the poly(A) tract of any specific mRNA may be detected by RNA filter hybridization after its removal from the body of the mRNA by a RNase H-catalyzed endonucleolytic cleavage in the 3' untranslated region. Using this method, we studied the modulation of the length of the poly(A) tract of rat vasopressin mRNA in vivo during changes in the levels of this mRNA resulting from a physiologic stimulus, osmotic stress. The poly(A) tract of hypothalamic vasopressin mRNA in hydrated rats was, quite remarkably, approximately 250 nucleotides in length, in contrast to that of somatostatin mRNA, which was approximately 30 nucleotides long. Vasopressin mRNA poly(A) tail length increased progressively from approximately 250 to approximately 400 nucleotides with the application of the hyperosmotic stimulus and declined to base line after its removal; somatostatin mRNA poly(A) tail length did not change during osmotic stress. The poly(A) tract length of total hypothalamic mRNA was between 35 and 140 nucleotides and also did not change with osmotic stress. Modulation of poly(A) tract length of specific mRNAs during stimulation of gene expression may provide an additional level of genetic regulation.

Determinants of mRNA stability in Dictyostelium discoideum amoebae: differences in poly(A) tail length, ribosome loading, and mRNA size cannot account for the heterogeneity of mRNA decay rates

As an approach to understanding the structures and mechanisms which determine mRNA decay rates, we have cloned and begun to characterize cDNAs which encode mRNAs representative of the stability extremes in the poly(A)+ RNA population of Dictyostelium discoideum amoebae. The cDNA clones were identified in a screening procedure which was based on the occurrence of poly(A) shortening during mRNA aging. mRNA half-lives were determined by hybridization of poly(A)+ RNA, isolated from cells labeled in a 32PO4 pulse-chase, to dots of excess cloned DNA. Individual mRNAs decayed with unique first-order decay rates ranging from 0.9 to 9.6 h, indicating that the complex decay kinetics of total poly(A)+ RNA in D. discoideum amoebae reflect the sum of the decay rates of individual mRNAs. Using specific probes derived from these cDNA clones, we have compared the sizes, extents of ribosome loading, and poly(A) tail lengths of stable, moderately stable, and unstable mRNAs. We found (i) no correlation between mRNA size and decay rate; (ii) no significant difference in the number of ribosomes per unit length of stable versus unstable mRNAs, and (iii) a general inverse relationship between mRNA decay rates and poly(A) tail lengths. Collectively, these observations indicate that mRNA decay in D. discoideum amoebae cannot be explained in terms of random nucleolytic events. The possibility that specific 3'-structural determinants can confer mRNA instability is suggested by a comparison of the labeling and turnover kinetics of different actin mRNAs. A correlation was observed between the steady-state percentage of a given mRNA found in polysomes and its degree of instability; i.e., unstable mRNAs were more efficiently recruited into polysomes than stable mRNAs. Since stable mRNAs are, on average, "older" than unstable mRNAs, this correlation may reflect a translational role for mRNA modifications that change in a time-dependent manner. Our previous studies have demonstrated both a time-dependent shortening and a possible translational role for the 3' poly(A) tracts of mRNA. We suggest, therefore, that the observed differences in the translational efficiency of stable and unstable mRNAs may, in part, be attributable to differences in steady-state poly(A) tail lengths.

Poly(A) shortening and degradation of the 3' A+U-rich sequences of human c-myc mRNA in a cell-free system

The early steps in the degradation of human c-myc mRNA were investigated, using a previously described cell-free mRNA decay system. The first detectable step was poly(A) shortening, which generated a pool of oligoadenylated mRNA molecules. In contrast, the poly(A) of a stable mRNA, gamma globin, was not excised, even after prolonged incubation. The second step, degradation of oligoadenylated c-myc mRNA, generated decay products whose 3' termini were located within the A+U-rich portion of the 3' untranslated region. These products disappeared soon after they were formed, consistent with rapid degradation of the 3' region. In contrast, the 5' region, corresponding approximately to c-myc exon 1, was stable in vitro. The data indicate a sequential degradation pathway in which 3' region cleavages occur only after most or all of the poly(A) is removed. To account for rapid deadenylation, we suggest that the c-myc poly(A)-poly(A)-binding protein complex is readily dissociated, generating a protein-depleted poly(A) tract that is no longer resistant to nucleases.

The vasopressin mRNA poly(A) tract is unusually long and increases during stimulation of vasopressin gene expression in vivo

We developed a method, termed an H-blot, by which the poly(A) tract of any specific mRNA may be detected by RNA filter hybridization after its removal from the body of the mRNA by a RNase H-catalyzed endonucleolytic cleavage in the 3' untranslated region. Using this method, we studied the modulation of the length of the poly(A) tract of rat vasopressin mRNA in vivo during changes in the levels of this mRNA resulting from a physiologic stimulus, osmotic stress. The poly(A) tract of hypothalamic vasopressin mRNA in hydrated rats was, quite remarkably, approximately 250 nucleotides in length, in contrast to that of somatostatin mRNA, which was approximately 30 nucleotides long. Vasopressin mRNA poly(A) tail length increased progressively from approximately 250 to approximately 400 nucleotides with the application of the hyperosmotic stimulus and declined to base line after its removal; somatostatin mRNA poly(A) tail length did not change during osmotic stress. The poly(A) tract length of total hypothalamic mRNA was between 35 and 140 nucleotides and also did not change with osmotic stress. Modulation of poly(A) tract length of specific mRNAs during stimulation of gene expression may provide an additional level of genetic regulation.

Determinants of mRNA stability in Dictyostelium discoideum amoebae: differences in poly(A) tail length, ribosome loading, and mRNA size cannot account for the heterogeneity of mRNA decay rates

As an approach to understanding the structures and mechanisms which determine mRNA decay rates, we have cloned and begun to characterize cDNAs which encode mRNAs representative of the stability extremes in the poly(A)+ RNA population of Dictyostelium discoideum amoebae. The cDNA clones were identified in a screening procedure which was based on the occurrence of poly(A) shortening during mRNA aging. mRNA half-lives were determined by hybridization of poly(A)+ RNA, isolated from cells labeled in a 32PO4 pulse-chase, to dots of excess cloned DNA. Individual mRNAs decayed with unique first-order decay rates ranging from 0.9 to 9.6 h, indicating that the complex decay kinetics of total poly(A)+ RNA in D. discoideum amoebae reflect the sum of the decay rates of individual mRNAs. Using specific probes derived from these cDNA clones, we have compared the sizes, extents of ribosome loading, and poly(A) tail lengths of stable, moderately stable, and unstable mRNAs. We found (i) no correlation between mRNA size and decay rate; (ii) no significant difference in the number of ribosomes per unit length of stable versus unstable mRNAs, and (iii) a general inverse relationship between mRNA decay rates and poly(A) tail lengths. Collectively, these observations indicate that mRNA decay in D. discoideum amoebae cannot be explained in terms of random nucleolytic events. The possibility that specific 3'-structural determinants can confer mRNA instability is suggested by a comparison of the labeling and turnover kinetics of different actin mRNAs. A correlation was observed between the steady-state percentage of a given mRNA found in polysomes and its degree of instability; i.e., unstable mRNAs were more efficiently recruited into polysomes than stable mRNAs. Since stable mRNAs are, on average, "older" than unstable mRNAs, this correlation may reflect a translational role for mRNA modifications that change in a time-dependent manner. Our previous studies have demonstrated both a time-dependent shortening and a possible translational role for the 3' poly(A) tracts of mRNA. We suggest, therefore, that the observed differences in the translational efficiency of stable and unstable mRNAs may, in part, be attributable to differences in steady-state poly(A) tail lengths.

Poly(A) shortening and degradation of the 3' A+U-rich sequences of human c-myc mRNA in a cell-free system

The early steps in the degradation of human c-myc mRNA were investigated, using a previously described cell-free mRNA decay system. The first detectable step was poly(A) shortening, which generated a pool of oligoadenylated mRNA molecules. In contrast, the poly(A) of a stable mRNA, gamma globin, was not excised, even after prolonged incubation. The second step, degradation of oligoadenylated c-myc mRNA, generated decay products whose 3' termini were located within the A+U-rich portion of the 3' untranslated region. These products disappeared soon after they were formed, consistent with rapid degradation of the 3' region. In contrast, the 5' region, corresponding approximately to c-myc exon 1, was stable in vitro. The data indicate a sequential degradation pathway in which 3' region cleavages occur only after most or all of the poly(A) is removed. To account for rapid deadenylation, we suggest that the c-myc poly(A)-poly(A)-binding protein complex is readily dissociated, generating a protein-depleted poly(A) tract that is no longer resistant to nucleases.

RNA processing and expression of an intron-encoded protein in yeast mitochondria: role of a conserved dodecamer sequence

The 3' ends of most Saccharomyces cerevisiae mitochondrial mRNAs terminate at a conserved dodecamer sequence, 5'-AAUAAUAUUCUU-3', of unknown function. We have studied the consequences of mutations within a dodecamer found in an 1,143-base-pair optional intron of the mitochondrial large (21S) rRNA gene on RNA processing. The dodecamer is situated at the 3' end of an expressed open reading frame (ORF) within that intron, and the mutations are two adjacent transversions that extend the intron ORF by 51 nucleotides. The strain harboring these mutations, L5-10-1, is defective in biased intron transmission in crosses to strains that lack the intron, as are other mutants which contain nucleotide changes within the ORF (I. G. Macreadie, R. M. Scott, A. R. Zinn, and R. A. Butow, Cell 41:395-402, 1985). However, unlike these other mutants, wild-type strains, or petites which retain the intron allele, L5-10-1 is defective in processing at the intron dodecamer. In addition, L5-10-1 lacks a prominent 2.7-kilobase RNA containing both intron and exon sequences and at least two of four RNAs that correspond to various forms of the excised intron. We propose that these RNAs, missing in L5-10-1 but present in all other strains examined, arise in part by processing at the intron dodecamer. In addition, in all strains examined, we have detected a novel processing activity in which precursor 21S rRNA transcripts are cleaved in the upstream exon, about 1,500 nucleotides from the 5' end of the RNA. This activity, together with 3' intron dodecamer cleavage, probably accounts for the 2.7-kilobase RNA species, a candidate for the mRNA for the intron-encoded protein.

DNA sequences downstream of the adenovirus type 2 fiber polyadenylation site contain transcription termination signals

The major late transcription unit of adenovirus type 2 (Ad2) terminates in a region near the end of the linear DNA genome at map units 98.2 to 100. Specific 3' ends mapping in the transcription termination region were detected in nuclear but not cytoplasmic RNA isolated at 16 to 18 h postinfection. Using S1 nuclease protection analysis, a major nuclear RNA species with a 3' terminus at map unit 98.9 was detected. With the use of recombinant expression vectors and run-on transcription in isolated nuclei, we demonstrated that the Ad2 sequences from map units 97.1 to 100, inserted into either the 5' or 3' untranslated sequences of the chloramphenicol acetyltransferase gene (cat), terminated transcription in transfected cells. Termination occurred only when the 97.1- to 100-map-unit sequence was in the same direction of transcription as the major late transcript and was not observed with Ad2 sequences upstream of map unit 97.1.

RNA processing and expression of an intron-encoded protein in yeast mitochondria: role of a conserved dodecamer sequence

The 3' ends of most Saccharomyces cerevisiae mitochondrial mRNAs terminate at a conserved dodecamer sequence, 5'-AAUAAUAUUCUU-3', of unknown function. We have studied the consequences of mutations within a dodecamer found in an 1,143-base-pair optional intron of the mitochondrial large (21S) rRNA gene on RNA processing. The dodecamer is situated at the 3' end of an expressed open reading frame (ORF) within that intron, and the mutations are two adjacent transversions that extend the intron ORF by 51 nucleotides. The strain harboring these mutations, L5-10-1, is defective in biased intron transmission in crosses to strains that lack the intron, as are other mutants which contain nucleotide changes within the ORF (I. G. Macreadie, R. M. Scott, A. R. Zinn, and R. A. Butow, Cell 41:395-402, 1985). However, unlike these other mutants, wild-type strains, or petites which retain the intron allele, L5-10-1 is defective in processing at the intron dodecamer. In addition, L5-10-1 lacks a prominent 2.7-kilobase RNA containing both intron and exon sequences and at least two of four RNAs that correspond to various forms of the excised intron. We propose that these RNAs, missing in L5-10-1 but present in all other strains examined, arise in part by processing at the intron dodecamer. In addition, in all strains examined, we have detected a novel processing activity in which precursor 21S rRNA transcripts are cleaved in the upstream exon, about 1,500 nucleotides from the 5' end of the RNA. This activity, together with 3' intron dodecamer cleavage, probably accounts for the 2.7-kilobase RNA species, a candidate for the mRNA for the intron-encoded protein.

mRNA polyadenylate-binding protein: gene isolation and sequencing and identification of a ribonucleoprotein consensus sequence

We identified and produced antibodies to the major proteins that interact with poly(A)+ RNAs in the yeast Saccharomyces cerevisiae. The major proteins which were cross-linked by UV light to poly(A)+ RNA in intact yeast cells had apparent molecular weights of 72,000, 60,000, and 50,000. The poly(A) segment of the RNA was selectively cross-linked to the 72,000-molecular-weight protein (72K protein). Mice immunized with purified UV-cross-linked RNA-protein (RNP) complexes produced antibodies to the three major RNP proteins. A yeast genomic DNA library constructed in the lambda gt11 expression vector was screened with the anti-RNP serum, and recombinant bacteriophage clones were isolated. One recombinant phage, lambda YPA72.1, bearing a 2.5-kilobase insert, produced a large beta-galactosidase-RNP fusion protein. Affinity-selected antibodies from the anti-RNP serum on this fusion protein recognized a single 72K protein which was cross-linked to the poly(A) segment of RNA in the intact cell. Furthermore, the fusion protein of lambda YPA72.1 had specific poly(A)-binding activity. Therefore, lambda YPA72.1 encodes the 72K poly(A)-binding protein. Immunofluorescence microscopy showed that this protein was localized in the cytoplasm. Hybrid-selected mRNA translated in vitro produced the 72K poly(A)-binding protein, and mRNA blot analysis detected a single 2.1-kilobase mRNA. DNA blot analysis suggested a single gene for the poly(A)-binding protein. DNA sequence analysis of genomic clones spanning the entire gene revealed a long open reading frame encoding a 64,272-molecular-weight protein with several distinct domains and repeating structural elements. A sequence of 11 to 13 amino acids is repeated three times in this protein. Strikingly, this repeated sequence (RNP consensus sequence) is highly homologous to a sequence that is repeated twice in a major mammalian heterogeneous nuclear RNP protein, A1. The conservation of the repetitive RNP consensus sequence suggests an important function and a common evolutionary origin for messenger RNP and heterogeneous nuclear RNP proteins.

Control of thymidylate synthase mRNA content and gene transcription in an overproducing mouse cell line

We studied the content and metabolism of thymidylate synthase mRNA in cultured mouse fibroblasts that were undergoing a serum-induced transition from the resting to growing state. The studies were performed with a 5-fluorodeoxyuridine-resistant 3T6 cell line (LU3-7) that over produces the enzyme and its mRNA about 50-fold and that regulates the expression of the thymidylate synthase gene in the same manner as the parental cell line. We have previously shown that the rate of synthesis of thymidylate synthase increases at least ninefold when the serum-stimulated cells traverse the S phase. Here we show, by Northern blot analysis, that thymidylate synthase mRNA increased 20- to 40-fold as cells progressed from resting to late S phase. About 85% of poly(A)+ thymidylate synthase mRNA was associated with polysomes at all times. The increase in thymidylate synthase poly(A)+ mRNA content was the result of an eightfold increase in the rate of production of this species, as shown by pulse-labeling studies. Pulse-chase analysis revealed that the half-life of thymidylate synthase poly(A)+ mRNA was similar in resting (9 h) and growing (7 h) cells. The rate of transcription of the thymidylate synthase gene, as determined in isolated nuclei, increased only by a factor of three to four during the S phase. Since the content of the message increased to a much greater extent than the rate of transcription of the gene, posttranscriptional controls must also play a role in regulating the content of thymidylate synthase mRNA under these conditions. Our results suggest that the cell may regulate the distribution of thymidylate synthase mRNA between a relatively stable poly(A)+ RNA species and a labile poly(A)- RNA species.

mRNA polyadenylate-binding protein: gene isolation and sequencing and identification of a ribonucleoprotein consensus sequence

We identified and produced antibodies to the major proteins that interact with poly(A)+ RNAs in the yeast Saccharomyces cerevisiae. The major proteins which were cross-linked by UV light to poly(A)+ RNA in intact yeast cells had apparent molecular weights of 72,000, 60,000, and 50,000. The poly(A) segment of the RNA was selectively cross-linked to the 72,000-molecular-weight protein (72K protein). Mice immunized with purified UV-cross-linked RNA-protein (RNP) complexes produced antibodies to the three major RNP proteins. A yeast genomic DNA library constructed in the lambda gt11 expression vector was screened with the anti-RNP serum, and recombinant bacteriophage clones were isolated. One recombinant phage, lambda YPA72.1, bearing a 2.5-kilobase insert, produced a large beta-galactosidase-RNP fusion protein. Affinity-selected antibodies from the anti-RNP serum on this fusion protein recognized a single 72K protein which was cross-linked to the poly(A) segment of RNA in the intact cell. Furthermore, the fusion protein of lambda YPA72.1 had specific poly(A)-binding activity. Therefore, lambda YPA72.1 encodes the 72K poly(A)-binding protein. Immunofluorescence microscopy showed that this protein was localized in the cytoplasm. Hybrid-selected mRNA translated in vitro produced the 72K poly(A)-binding protein, and mRNA blot analysis detected a single 2.1-kilobase mRNA. DNA blot analysis suggested a single gene for the poly(A)-binding protein. DNA sequence analysis of genomic clones spanning the entire gene revealed a long open reading frame encoding a 64,272-molecular-weight protein with several distinct domains and repeating structural elements. A sequence of 11 to 13 amino acids is repeated three times in this protein. Strikingly, this repeated sequence (RNP consensus sequence) is highly homologous to a sequence that is repeated twice in a major mammalian heterogeneous nuclear RNP protein, A1. The conservation of the repetitive RNP consensus sequence suggests an important function and a common evolutionary origin for messenger RNP and heterogeneous nuclear RNP proteins.

An analysis of the rate of metallothionein mRNA poly(A)-shortening using RNA blot hybridization

A progressive reduction in the size of rat metallothionein-1 mRNA following induction by copper chloride or dexamethasone was demonstrated on RNA blots, and was shown to be due to shortening of the poly(A)-tail. The rate of poly(A) removal was the same in rat liver and kidney following copper chloride induction, in rat liver following dexamethasone induction, and in mouse liver following copper chloride induction. In mouse liver metallothionein-1 and 2 mRNAs were shortened at the same rate. The reduction of the poly(A) tail was more rapid in the first 5 hours (approximately 20 nucleotides/h) but much slower (approximately 3 nucleotides/h) after the poly(A)-tail had been reduced to about 60 residues. Metallothionein mRNA molecules with poly(A) tail sizes less than 30-40 nucleotides were not observed. Exonuclease digestion of the poly(A)-tail is suggested, at least in the initial rapid phase. It is hypothesized that poly(A)-tails longer than 30 are required for mRNA stability and that much longer poly(A) tails may give newly synthesized mRNA molecules a competitive advantage in protein synthesis.

Control of thymidylate synthase mRNA content and gene transcription in an overproducing mouse cell line

We studied the content and metabolism of thymidylate synthase mRNA in cultured mouse fibroblasts that were undergoing a serum-induced transition from the resting to growing state. The studies were performed with a 5-fluorodeoxyuridine-resistant 3T6 cell line (LU3-7) that over produces the enzyme and its mRNA about 50-fold and that regulates the expression of the thymidylate synthase gene in the same manner as the parental cell line. We have previously shown that the rate of synthesis of thymidylate synthase increases at least ninefold when the serum-stimulated cells traverse the S phase. Here we show, by Northern blot analysis, that thymidylate synthase mRNA increased 20- to 40-fold as cells progressed from resting to late S phase. About 85% of poly(A)+ thymidylate synthase mRNA was associated with polysomes at all times. The increase in thymidylate synthase poly(A)+ mRNA content was the result of an eightfold increase in the rate of production of this species, as shown by pulse-labeling studies. Pulse-chase analysis revealed that the half-life of thymidylate synthase poly(A)+ mRNA was similar in resting (9 h) and growing (7 h) cells. The rate of transcription of the thymidylate synthase gene, as determined in isolated nuclei, increased only by a factor of three to four during the S phase. Since the content of the message increased to a much greater extent than the rate of transcription of the gene, posttranscriptional controls must also play a role in regulating the content of thymidylate synthase mRNA under these conditions. Our results suggest that the cell may regulate the distribution of thymidylate synthase mRNA between a relatively stable poly(A)+ RNA species and a labile poly(A)- RNA species.

Transcription of herpes simplex virus tk sequences under the control of wild-type and mutant human RNA polymerase I promoters

We studied RNA polymerase I transcription in cells transfected with a plasmid, prHuTK, containing the herpes simplex virus tk gene fused to a human rRNA promoter. Primer extension analysis of tk RNA isolated from COS cells transfected with prHuTK reveals that transcription from the RNA polymerase I promoter is highly efficient and initiates at the same position used for the synthesis of endogenous rRNA in HeLa cells. The RNA products derived from prHuTK are distinguishable from normal RNA polymerase II transcripts of tk in that they are not polyadenylated, are extremely unstable, and are found predominantly in the nucleus. Moreover, the transcription observed is resistant to 300 micrograms of alpha-amanitin per ml. These results strongly suggest that prHuTK transcription is under the control of the human rRNA promoter and RNA polymerase I. To further characterize the activity of the human rDNA promoter in vivo, a series of 5' and 3' deletion mutants was tested in this transfection assay. The deletion analysis indicates that a core region of ca. 40 base pairs overlapping the initiation site is critical for transcription. In addition, a region between nucleotides -234 and -131 upstream from the core sequence serves to modulate the efficiency of transcription. Insertion into prHuTK of additional ribosomal nontranscribed spacer DNA or the simian virus 40 enhancer element has no apparent effect on the promoter activity. Surprisingly, RNA polymerase II transcripts synthesized at low levels from two start sites within the core control element of the wild-type RNA polymerase I promoter are activated upon deletion of upstream RNA polymerase I promoter sequences. However, these RNA polymerase II transcripts are not expressed from the endogenous rRNA promoter.

Transcription of herpes simplex virus tk sequences under the control of wild-type and mutant human RNA polymerase I promoters

We studied RNA polymerase I transcription in cells transfected with a plasmid, prHuTK, containing the herpes simplex virus tk gene fused to a human rRNA promoter. Primer extension analysis of tk RNA isolated from COS cells transfected with prHuTK reveals that transcription from the RNA polymerase I promoter is highly efficient and initiates at the same position used for the synthesis of endogenous rRNA in HeLa cells. The RNA products derived from prHuTK are distinguishable from normal RNA polymerase II transcripts of tk in that they are not polyadenylated, are extremely unstable, and are found predominantly in the nucleus. Moreover, the transcription observed is resistant to 300 micrograms of alpha-amanitin per ml. These results strongly suggest that prHuTK transcription is under the control of the human rRNA promoter and RNA polymerase I. To further characterize the activity of the human rDNA promoter in vivo, a series of 5' and 3' deletion mutants was tested in this transfection assay. The deletion analysis indicates that a core region of ca. 40 base pairs overlapping the initiation site is critical for transcription. In addition, a region between nucleotides -234 and -131 upstream from the core sequence serves to modulate the efficiency of transcription. Insertion into prHuTK of additional ribosomal nontranscribed spacer DNA or the simian virus 40 enhancer element has no apparent effect on the promoter activity. Surprisingly, RNA polymerase II transcripts synthesized at low levels from two start sites within the core control element of the wild-type RNA polymerase I promoter are activated upon deletion of upstream RNA polymerase I promoter sequences. However, these RNA polymerase II transcripts are not expressed from the endogenous rRNA promoter.

Physical change in cytoplasmic messenger ribonucleoproteins in cells treated with inhibitors of mRNA transcription

Exposure of intact cells to UV light brings about cross-linking of polyadenylated mRNA to a set of cytoplasmic proteins which are in direct contact with the mRNA in vivo. Substantial amounts of an additional protein of molecular weight 38,000 (38K) become cross-linked to the mRNA when cells are treated with inhibitors of mRNA synthesis (actinomycin D, camptothecin, and 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole) or after infection with vesicular stomatitis virus. Cordycepin, which inhibits polyadenylation but not mRNA synthesis, has no such effect. Inhibitors of protein synthesis and of rRNA synthesis are also without effect on 38K cross-linking to mRNA. The onset of the effect of inhibitors of mRNA synthesis on the UV cross-linkable interaction between mRNA and 38K is rapid and reaches a maximal level in less than 60 min, and it is completely and rapidly reversible. In cells treated with actinomycin D, the amount of 38K which becomes cross-linked to mRNA is proportional to the extent of inhibition of mRNA synthesis. The association of 38K with mRNA during transcriptional arrest does not require protein synthesis because simultaneous treatment with the protein synthesis inhibitor emetine does not interfere with it. The effectors which promote the interaction of 38K with mRNA do not affect the proteins which are in contact with polyadenylated heterogeneous nuclear RNA and do not markedly affect protein synthesis in the cell. The 38K protein can be isolated with the polyribosomal polyadenylated fraction from which it was purified, and monoclonal antibodies against it were prepared. Immunofluorescence microscopy shows mostly cytoplasmic and some nuclear staining. These observations demonstrate that commonly used inhibitors of transcription affect the physical state of messenger ribonucleoproteins in vivo.

Saccharomyces cerevisiae killer virus transcripts contain template-coded polyadenylate tracts

The M double-stranded RNA component of type 1 killer strains of the yeast Saccharomyces cerevisiae contains an internal 200-base pair adenine- and uracil-rich region. The plus strands of this viral genomic RNA contain an internal adenine-rich region which allows these strands to bind to polyuridylate-Sepharose as tightly as do polyadenylated RNAs with 3'-terminal polyadenylated tracts of 70 to 100 residues. Internal template coding of an adenine-rich tract in positive polarity in vivo and in vitro transcripts of M double-stranded RNA may serve as an alternate method of transcript polyadenylation. The 3'-terminal residue of the in vitro m transcript is a non-template-encoded purine residue. The 5' terminus of this transcript is involved in a stem-and-loop structure which includes an AUG initiation codon, along with potential 18S and 5.8S rRNA binding sites. Except for the 3'-terminal residue, transcription in in vitro shows complete fidelity.

Ascorbate stimulation of PAT cells causes an increase in transcription rates and a decrease in degradation rates of procollagen mRNA

Procollagen alpha 2 (I) mRNA can be induced congruent to 6-fold in primary avian tendon (PAT) cells on addition of ascorbate to the culture medium. Previously, we have shown that the induction is linear after a 12 h lag and requires a total of 60-72 h to achieve maximum levels. We have now investigated in more detail the changes that have occurred in the metabolism of procollagen mRNA in fully induced cells to account for the observed induction. Ascorbate was found to triple the rate of procollagen gene transcription. In addition, there was a stabilization of the mRNA causing the half-life to increase from 10.5 h to 20 h. The increased stability of the procollagen mRNA, however, did not correlate with its ability to bind to oligo (dT)-cellulose. Since a 3-fold change in transcription rates and a 2-fold increase in half-life would account for the 6-fold overall increase in procollagen mRNA levels, we conclude that these are the primary alterations caused by ascorbate addition that give rise to the specific increase in procollagen mRNA.

Physical change in cytoplasmic messenger ribonucleoproteins in cells treated with inhibitors of mRNA transcription

Exposure of intact cells to UV light brings about cross-linking of polyadenylated mRNA to a set of cytoplasmic proteins which are in direct contact with the mRNA in vivo. Substantial amounts of an additional protein of molecular weight 38,000 (38K) become cross-linked to the mRNA when cells are treated with inhibitors of mRNA synthesis (actinomycin D, camptothecin, and 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole) or after infection with vesicular stomatitis virus. Cordycepin, which inhibits polyadenylation but not mRNA synthesis, has no such effect. Inhibitors of protein synthesis and of rRNA synthesis are also without effect on 38K cross-linking to mRNA. The onset of the effect of inhibitors of mRNA synthesis on the UV cross-linkable interaction between mRNA and 38K is rapid and reaches a maximal level in less than 60 min, and it is completely and rapidly reversible. In cells treated with actinomycin D, the amount of 38K which becomes cross-linked to mRNA is proportional to the extent of inhibition of mRNA synthesis. The association of 38K with mRNA during transcriptional arrest does not require protein synthesis because simultaneous treatment with the protein synthesis inhibitor emetine does not interfere with it. The effectors which promote the interaction of 38K with mRNA do not affect the proteins which are in contact with polyadenylated heterogeneous nuclear RNA and do not markedly affect protein synthesis in the cell. The 38K protein can be isolated with the polyribosomal polyadenylated fraction from which it was purified, and monoclonal antibodies against it were prepared. Immunofluorescence microscopy shows mostly cytoplasmic and some nuclear staining. These observations demonstrate that commonly used inhibitors of transcription affect the physical state of messenger ribonucleoproteins in vivo.

Saccharomyces cerevisiae killer virus transcripts contain template-coded polyadenylate tracts

The M double-stranded RNA component of type 1 killer strains of the yeast Saccharomyces cerevisiae contains an internal 200-base pair adenine- and uracil-rich region. The plus strands of this viral genomic RNA contain an internal adenine-rich region which allows these strands to bind to polyuridylate-Sepharose as tightly as do polyadenylated RNAs with 3'-terminal polyadenylated tracts of 70 to 100 residues. Internal template coding of an adenine-rich tract in positive polarity in vivo and in vitro transcripts of M double-stranded RNA may serve as an alternate method of transcript polyadenylation. The 3'-terminal residue of the in vitro m transcript is a non-template-encoded purine residue. The 5' terminus of this transcript is involved in a stem-and-loop structure which includes an AUG initiation codon, along with potential 18S and 5.8S rRNA binding sites. Except for the 3'-terminal residue, transcription in in vitro shows complete fidelity.

Polyadenylic acid addition sites in the adenovirus type 2 major late transcription unit

The cytoplasmic mRNAs which are transcribed from the major late adenovirus promoter can be arranged into five 3'-coterminal families, L1 to L5. We have defined the polyadenylation sites of the mRNAs that belong to the five families at the nucleotide level. From the results, the following conclusions can be made. (i) The hexanucleotide sequence AAUAAA is present at the 3' end of all late adenovirus type 2 mRNAs and precedes the site of polyadenylation by 12 to 30 nucleotides. (ii) Between one and three A residues are present in the genomic sequence at the polyadenylation site. (iii) A sequence with the composition (T)n (A)p (T)q (n, p, q greater than or equal to 1) is found 4 to 24 nucleotides beyond all the adenovirus-specific polyadenylation sites except the 3'-coterminal family L4. This sequence is also found beyond many cellular polyadenylation sites. (iv) The L1 and L2 polyadenylation sites are very similar in structure. The other polyadenylation sites show no apparent sequence relationship, except for the hexanucleotide sequence.

Localization of the adenovirus E1Aa protein, a positive-acting transcriptional factor, in infected cells infected cells

The function of the adenovirus E1Aa protein (the product of the 13S E1A mRNA) during a productive viral infection is to activate transcription of the six early viral transcription units. To study the mechanism of action of this protein, a peptide which was 13 amino acids long and had a sequence unique to the protein product of the adenovirus 13S E1A mRNA (pE1Aa) was coupled to keyhole limpet hemocyanin and used to raise an antibody in rabbits. The resulting antiserum was specific to this protein and did not react with the protein product of the 12S E1A mRNA, which shares considerable sequence with the E1Aa protein. This antiserum was used to probe for the E1Aa protein in situ by indirect immunofluorescence and in extracts of infected HeLa cells. We found that the protein was associated with large cellular structures both in the nucleus and in the cytoplasm. The nuclear form of the protein was analyzed further and was found to purify with the nuclear matrix.

Localization of the adenovirus E1Aa protein, a positive-acting transcriptional factor, in infected cells infected cells

The function of the adenovirus E1Aa protein (the product of the 13S E1A mRNA) during a productive viral infection is to activate transcription of the six early viral transcription units. To study the mechanism of action of this protein, a peptide which was 13 amino acids long and had a sequence unique to the protein product of the adenovirus 13S E1A mRNA (pE1Aa) was coupled to keyhole limpet hemocyanin and used to raise an antibody in rabbits. The resulting antiserum was specific to this protein and did not react with the protein product of the 12S E1A mRNA, which shares considerable sequence with the E1Aa protein. This antiserum was used to probe for the E1Aa protein in situ by indirect immunofluorescence and in extracts of infected HeLa cells. We found that the protein was associated with large cellular structures both in the nucleus and in the cytoplasm. The nuclear form of the protein was analyzed further and was found to purify with the nuclear matrix.