Isolation of chicken hemoglobin mRNA and synthesis of complementary DNA

Avian retroviral vectors derived from avian defective leukemia virus: role of the translational context of the inserted gene on efficiency of the vectors

We have constructed retroviral vectors derived from the genome of avian erythroblastosis virus ES4 (AEV ES4). The neo selectable gene was substituted for the original v-erbA or v-erbB oncogenes of AEV, either in the same or in a different reading frames. Recombinant retrovirus were rescued and used to infect chicken embryo fibroblasts or quail QT6 cells. When the neo gene was inserted in the same reading frame as the original oncogene, we obtained (1) a high level of expression of the neo gene, (2) a balanced ration of both genomic and subgenomic RNAs, and (3) high titer recombinant viruses. Conversely, when the neo gene was inserted in a reading frame different from that of the original oncogene, we observed (1) a very low level of expression of the neo protein, (2) a predominance of the viral transcript used as translational template for the neo protein synthesis, and (3) low titer recombinant viruses. One of the vectors was used to transfer a human delta-globin gene into avian cells in culture without detectable rearrangement of this gene, but exhibited a deletion within the conserved noncoding region located between the two original oncogenes. Our data provide information for further construction of double expression vectors. Furthermore, three of the vectors would provide helpful tools to identify genetic elements of the virus genome involved in splicing regulation.

Messenger RNA content and complexity in normal and overloaded rat heart

Cardiac overload was studied in rats by abdominal aortic constriction, which increased the left ventricular weight by 59% after 12 days. During the transition, which precedes the compensatory hypertrophy, both total RNA and poly(A)-containing messenger RNA increased. The concentration of these polynucleotides peaked by day 4 after constriction, rising from 1.27 +/- 0.3 to 1.88 +/- 0.2 mg g-1 fresh weight for total RNA, and from 38 +/- 24 to 62 +/- 12 micrograms g-1 fresh weight for poly(A)-containing RNA, and returned to normal by day 12. However, the total amount per ventricle of both RNAs remained high. Poly(A)-containing RNA prepared from normal heart was hybridized to its cDNA copy. These results were expressed as the percentage of hybridization vs. the log 10 of the product of the poly(A)-containing RNA concentration and the time (Rot), and in computer analysis were described by division into three different frequency components. In normal hearts, the Rot 1/2 values of these components were, respectively, 3.98 X 10(-3), 0.338 and 21.380 mol.s.1(-1), which correspond to 2-3, 240 and 12,200 different sequences that were copied 22,000-33,000, 310 and 5 times, respectively. Four and 30 days after banding there was a harmonious enhancement of the number of the copies without any change in the number of different sequences, and the three different hybridization curves were superimposed. In conclusion, cardiac overload raises the poly(A)-containing RNA concentration, probably by stimulating transcription, but no major changes occur in any of the frequency classes.

Synthesis of messenger-like RNA in avian erythrocyte nuclei

Cell ghosts have been prepared from mature chicken erythrocytes using 0.05% saponin. Such preparations are capable of incorporating label from [3H]UTP and provide a system, where the nucleus is permeable to nucleotides and macromolecules, for studying the low-level RNA synthesis characteristic of these cells. RNase A (50 micrograms/ml) eliminated all radioactivity binding to DE-81 filters, indicating that the product was RNA; and DNase (10 micrograms/ml) and actinomycin D (10 micrograms/ml) each inhibited UMP incorporation by 70%, suggesting that the synthesis was DNA-dependent. Polymerization was inhibited 90% by 0.1 microgram/ml alpha-amanitin, and maximum synthesis occurred in the presence of high salt (0.175 M KCl) and Mn2+ (0.5 mM). Polyacrylamide gel electrophoresis indicated that the newly synthesized RNA was heterogeneous in size, having a distribution from 5 to 60 S with a significant fraction migrating as 8-12 S. Approximately 15% of the total RNA was bound by an oligo(dT)-cellulose column, suggesting that some RNA processing was occurring, although attempts to detect the incorporation of label from [alpha-32P]GTP into a 5'-cap structure were unsuccessful. In comparison to RNA synthesis in reticulocyte nuclei, both the rate and extent of transcription in erythrocyte nuclei were much reduced. Moreover, about 25-30% of the reticulocyte nascent RNA was released from the nuclei during a 60-min incubation, while no release was observed for the erythrocyte nuclei. Hybridization of radiolabeled RNA to excess chicken DNA indicated that the majority (80%) of the in vitro transcripts were complementary to unique sequence DNA (C0t1/2 = 4.5 X 10(3)). When RNA synthesized by either erythrocyte or reticulocyte nuclei was hybridized to cDNA complementary to reticulocyte polysomal mRNA, about 8% of the reticulocyte nuclear RNA but less than 1% of the erythrocyte nuclear RNA were resistant to RNase A digestion. Taken together, these data suggest that nuclei prepared by saponin lysis of chicken erythrocytes synthesize messenger-like RNA via endogenous polymerase II activity. A fraction of this RNA is polyadenylated but contains few, if any, globin sequences or other transcripts found on reticulocyte polysomes.

Biosynthesis of cat hemoglobins: translation of poly(A)-RNA from animals of various HbA/HbB phenotypes

The molecular basis for the genetic control of variable proportions of the two hemoglobins in domestic cat blood was investigated. Both major hemoglobins of cat blood, HbA (alpha 2 beta A2) and HbB (alpha 2 beta B2), were synthesized in an mRNA-dependent rabbit reticulocyte system using poly(A)-RNA from cat reticulocyte polysomes as the source of the message. The relative amounts of HbA and HbB synthesized in the system were a function of the HbA/HbB phenotype of the cat from which the reticulocytes and poly(A)-RNA were obtained. Higher ratios of HbA/HbB synthesis were found when the source of poly(A)-RNA was the polysomes from a 90/10 (HbA/HbB) phenotype than when it was from a 50/50 (HbA/HbB) phenotype. These results indicate that the variable proportions of HbA and HbB found in the blood of different members of the cat population result from the genetic control of the relative amounts of functional beta A and beta B mRNA.

Formation of a 22S mRNA X rRNA X protein complex during translation of globin messenger RNA

Poly(A)-rich RNA was isolated from rabbit reticulocyte polyribosomes by affinity chromatography on oligo(dT)-cellulose and fractionated in sucrose gradients under non-denaturing conditions. Most of the translatable RNA sedimented in sucrose gradients both as free 9S mRNA and as a 22S complex containing 18S ribosomal RNA and a protein of Mr 66 000. The complex was characterized by identification of the translation products. Experiments with both labelled globin mRNA and Mr-66 000 protein indicate that the complex is not an artefact, but rather that it is formed during the initiation of protein synthesis. The Mr-66 000 protein appears to be a component of the 48S pre-initiation complex and recycles before 80S complex formation.

An improved purification and further characterization of the messenger ribonucleic acid for the fatty acid synthetase from rat liver

High purity fatty acid synthetase mRNA has been prepared from rat liver. The translational purity of the mRNA preparation was at least 27% as judged by the percentage of the radioactivity incorporated into acid-insoluble material that was precipitated by anti-fatty acid synthetase antibody. The specific activity of the mRNA was 220-times greater than that reported previously from this laboratory [1]. The large increase in the specific activity was achieved by the repeated use of high resolution linear-log sucrose density gradient centrifugation and the removal of 28 S rRNA by Sepharose 4B chromatography, as well as by the optimization of the K+ concentration (160 mM) in the reticulocyte lysate translation system. The mRNA preparation showed a single major band on agarose gel electrophoresis under denaturing conditions, and the translational activity of the fatty acid synthetase mRNA on the gel was found to coincide with this band. The molecular weight of the fatty acid synthetase mRNA is 2.5.10(6) Da. The mRNA directed the synthesis of fatty acid synthetase with a molecular weight indistinguishable from that of the authentic enzyme subunit (Mr = 240 000). The copurification of the translation product and authentic enzyme revealed that the fatty acid synthetase polypeptides synthesized in the reticulocyte lysate system are assembled in vitro into dimers, the native form of the enzyme.

Histone H5 messenger RNA is polyadenylated

In most known systems, histone mRNA lacks the poly(A) sequence at the 3' end of the molecule typical of most mRNAs. Furthermore, the synthesis of histones, unlike that of most proteins, is tightly coupled to DNA synthesis. Nevertheless, histone synthesis occurs in amphibian oocytes in the absence of DNA synthesis. Moreover, it has recently been found that in amphibian oocytes most of the histone mRNA is polyadenylated, and the polyadenylate is probably removed during maturation of the oocyte. Histone H5, an H1-like tissue-specific histone occurring only in nucleated erythrocytes, is also atypical in that it is synthesised in the absence of DNA synthesis during maturation of the red blood cells. We report here that H5 mRNA is polyadenylated.

The structure and transcription of four linked rabbit beta-like globin genes

Rabbit chromosomal DNA contains a cluster of four linked beta-like globin genes arranged in the orientation 5'-beta 4-(8kb)-beta 3-(5 kb)-beta 2-(7-kb)-beta 1-3'. Determination of the nucleotide sequence of gene beta 1 confirms that this gene corresponds to the second type of two common co-dominant alleles encoding the adult beta-globin chain. With the exception of two nucleotide substitutions in the large intervening sequence (intron), the intron and flanking sequences are identical with the nucleotide sequence of the first type determined by Weissmann et al. (1979). A 14S polyadenylated transcript containing large intron sequences (possibly a mRNA precursor) is detected in the bone marrow cells of anemic rabbits. Gene beta 2 has limited sequence homology to adult and embryonic beta-globin probes and lacks a detectable mRNA transcript in the erythropoietic tissues examined. It contains at least one intervening sequence analogous to the large intron in gene beta 1. Genes beta 3 and beta 4 both contain an intron of 0.8 kb. Partial DNA sequence analysis indicates that the large intron in beta 4 is located between codons for amino acids lysine and leucine in an analogous position to that of the large intron in beta 1. In addition, a second smaller intron interrupts the 5' coding sequences of gene beta 4. Both genes beta 3 and beta 4 are transcribed in embryonic globin-producing cells. Their DNA sequence homology is limited, however, to a segment of approximately 0.2 kb located on the 5' side of the large intron.

Heterogeneity of genetic loci in chickens: analysis of endogenous viral and nonviral genes by cleavage of DNA with restriction endonucleases

Restriction endonucleases can be used to define the structure and position of genetic loci for which specific molecular hybridization reagents are available. We have used this approach to compare 18 chicken embryos with respect to several cellular genes; endogenous viral DNA related to the replicative genes of avian sarcoma virus (ASV) or to RAV-O, an endogenous virus of chickens; and sequences related to the transforming (src) gene of ASV. Each cellular gene eas remarkably homogeneous within our test population. We found little or no variation in globin and ovomucoid genes; ovalbumin and transferrin (with one exception) showed variation which is probably allelic in nature. The endogenous viral DNA which has homology with RAV-O was found at several different positions in host DNA and its structure resembled that of proviruses acquired by experimental infection, with sequences from both ends of viral RNA repeated near both ends of viral DNA. Within the population of 18 chickens, one endogenous provirus was always present, whereas the several other proviruses were each found in only a few members of this group. However, screening of additional chickens identified individuals lacking the provirus common to the initial 18 animals surveyed; in at least one embryo no RAV-O-related DNA was detected. These findings suggest that the endogenous RAV-O-related sequences have entered the germ line by relatively recent infection and are still segregating in several contemporary chicken flocks. The sequences in the chicken genome which have homology with the src gene of ASV are invariant from bird to bird and in this sense resemble a cellular gene rather than a viral sequence.

Procollagen complementary DNA, a probe for messenger RNA purification and the number of type I collagen genes

Type I procollagen mRNAs were separated from contaminating low-abundance messenger and nuclear RNAs by chromatography over Sepharose 4B in 0.65 M NaCl at room temperature. All of 27S rRNA and four-fifths of procollagen mRNAs bind to Sepharose under these conditions, while 18S rRNA and about three-fourths of other poly(A)-containing RNAs do not bind. AMV reverse transcriptase was used to prepare complementary DNA to procollagen mRNA at each purification step. Hybridization studies, in RNA excess, were carried out to establish the enrichment at each step both with respect to total RNA and to poly(A)-containing RNA. While "purified" procollagen mRNA preparations still consist of about 50% 27S rRNA, over 80% of cDNA prepared from it back hybridizes to its template at a log of cr0t1/2 of -1.9. This type I procollagen cDNA hybridizes in DNA excess to DNA isolated from chicken erythrocytes and from embryonic chick calvaria at a log c0t1/2 of 3.1, demonstrating that procollagen cDNA is complementary to unique gene sequences in both tissues and that procollagen genes are not reiterated.