Isolation and characterization of purified rat casein messenger ribonucleic acids

Human alpha 1-antitrypsin expression in Xenopus oocytes. Secretion of the normal (PiM) and abnormal (PiZ) forms

Injection of equivalent amounts of normal (PiMM) or abnormal (PiZZ) alpha 1-antitrypsin mRNA into Xenopus oocytes resulted in secretion of both the normal and abnormal alpha 1-antitrypsin. A much lower proportion of the abnormal protein was secreted, and the Z alpha 1-antitrypsin that was not secreted accumulated within the cell in a high-mannose form. The time taken for secretion of the normal and abnormal proteins was identical. Both the secreted and intracellular alpha 1-antitrypsin synthesized by oocytes were functionally active.

Isolation and characterization of the glucose-6-phosphate dehydrogenase gene of Drosophila melanogaster

To investigate the molecular basis of dosage compensation in Drosophila, a recombinant lambda phage containing the Drosophila melanogaster glucose-6-phosphatase dehydrogenase (G6PD) gene was isolated by differential screening of a Drosophila genomic lambda library with poly(A)+RNA obtained from polyribosomes enriched for or depleted of G6PD mRNA sequences. Of 44 000 plaques screened, a single phage, lambda DmG21, showed hybridization with the enriched poly(A)+RNA but not the depleted one. Confirmation that the Drosophila DNA fragment cloned in lambda DmG21 contains the G6PD gene sequence is based on the following observations. lambda DmG21 DNA shows hybridization only to the 18D region of the salivary gland X-chromosome, which is the known cytological locus for the G6PD gene. In vitro translation of the poly(A)+mRNA selected by hybridization to lambda DmG21 DNA sequences shows a polypeptide product of apparent Mr 55 000, identical to that of the monomeric unit of G6PD. When the putative coding sequence of G6PD is cloned into the expression vector lambda gt11, recombinant plaques are recognized by anti-G6PD immunoglobulin. A transcriptional map of the G6PD gene shows that it is divided into two exons, 0.9 kb (exon I) and 1.8 kb (exon II) long, which are separated by a 2.4-kb intron. The G6PD mRNA is 2.0 kb in length and the steady-state level of the mRNA is similar in both sexes. Measurement of the copy number of the G6PD gene in males and females shows the gene to be present once per X-chromosome in both sexes. No amplification of the gene sequence was observed in males. These results are, therefore, in agreement with the previous suggestion that dosage compensation is the result of enhanced transcription of X-linked genes in males.

Biochemical mapping of the simian rotavirus SA11 genome

Biochemical mapping experiments of the simian rotavirus SA11 genome were performed to determine which double-stranded RNA segment coded for each of the viral polypeptides. Viral RNA transcripts were synthesized in vitro by using the endogenous viral RNA polymerase and fractionated by electrophoresis in acid-urea agarose gels. The fractionated transcripts were translated in two cell-free systems: micrococcal nuclease-treated reticulocyte lysates and wheat germ extracts. The polypeptide products were identified by polyacrylamide gel electrophoresis and partial peptide analysis and compared with polypeptides synthesized in infected cells or found in purified virus. The RNA segment that coded for each transcript was determined by hybridization of the fractionated transcripts to the double-stranded RNA genome and analysis of the hybrids by electrophoresis in polyacrylamide gels. Primary gene products were assigned for 10 of the rotavirus transcripts and 10 of the double-stranded RNA segments. The coding assignments are as follows: the inner-capsid polypeptides, VP1, VP2, and VP6, were assigned to segments 1, 2, and 6, respectively; the major outer-capsid polypeptides, VP3 and VP7, were assigned to segments 4 and 9, respectively; segments 5, 7, and 8 coded for nonstructural polypeptides with molecular weights of 53,000, 34,000, and 35,000, respectively; segment 10 coded for the 20,000-molecular-weight precursor to the 29,000-molecular-weight glycosylated nonstructural polypeptide; and segment 11 coded for a 26,000-molecular-weight polypeptide that may be the precursor to the minor outer-capsid polypeptide VP9. Several methods were used to determine the product of gene segment 3, and the problems associated with the identification of this gene product are discussed.

Translation and processing of normal (PiMM) and abnormal (PiZZ) human alpha 1-antitrypsin

Human liver mRNA isolated from subjects phenotyped as homozygous PiMM or PiZZ alpha 1-antitrypsin, was translated in a reticulocyte cell-free system, and alpha 1-antitrypsin identified by immunoprecipitation. In the presence of dog pancreas membranes the translated alpha 1-antitrypsin appeared as a larger product. Treatment with endo-beta-N-glucosaminidase yielded a protein smaller than the reticulocyte translated product, presumably due to removal of the N-terminal signal sequence by membranes and sugar residues by endo-beta-N-glucosaminidase. Quantitation of alpha 1-antitrypsin translated from PiMM and PiZZ livers suggests that both mRNA species were present at the same cellular concentration, and that processing to the core glycosylation stage proceeded at identical rates.

Sequence of rat alpha- and gamma-casein mRNAs: evolutionary comparison of the calcium-dependent rat casein multigene family

The complete sequences of rat alpha- and gamma-casein mRNAs have been determined. The 1402-nucleotide alpha- and 864-nucleotide gamma-casein mRNAs both encode 15 amino acid signal peptides and mature proteins of 269 and 164 residues, respectively. Considerable homology between the 5' non-coding regions, and the regions encoding the signal peptides and the phosphorylation sites, in these mRNAs as compared to several other rodent casein mRNAs, was observed. Significant homology was also detected between rat alpha- and bovine alpha s1-casein. Comparison of the rodent and bovine sequences suggests that the caseins evolved at about the time of the appearance of the primitive mammals. This may have occurred by intragenic duplication of a nucleotide sequence encoding a primitive phosphorylation site, -(Ser)n-Glu-Glu-, and intergenic duplication resulting in the small casein multigene family. A unique feature of the rat alpha-casein sequence is an insertion in the coding region containing 10 repeated elements of 18 nucleotides each. This insertion appears to have occurred 7-12 million years ago, just prior to the divergence of rat and mouse.

Separation and characterization of low-molecular-weight nuclear RNA species that inhibit cell-free protein synthesis

Various RNA fractions were isolated from nuclei of 12-day lactating rat mammary glands and examined for their ability to inhibit cell-free protein synthesis. Although total nuclear RNA was generally inactive, material contained in the poly(A)+ nuclear RNA fraction and the low-molecular-weight RNA derived from total nuclear RNA by sucrose gradient centrifugation, inhibited the translation of several mRNAs but not poly(U) or poly(A). Separation of the small nuclear RNAs by preparative polyacrylamide-urea gel electrophoresis allowed the identification of at least three active inhibitor RNA species. These differed both with respect to their ability to inhibit protein synthesis, and in their mechanism of action. While two of the RNA species inhibited elongation the other inhibited initiation of protein synthesis.

In vitro synthesis of M and Z forms of human alpha 1-antitrypsin

mRNA was prepared from autopsy liver samples from a homozygote for alpha 1-antitrypsin deficiency (PiZZ) and from a normal (PiMM) subject. Both preparations gave equivalent synthesis of alpha 1-antitrypsin in a wheat germ cell-free system. This suggests that the deficiency of plasma alpha 1-antitrypsin associated with the Z variant is due to a failure of processing and secretion of the protein rather than of its synthesis. It is likely that it is the resultant intracellular accumulation of the Z protein rather than a deficiency of protease inhibitor that is the primary cause of the liver pathology associated with this variant.

Rat beta casein cDNA: sequence analysis and evolutionary comparisons

The complete sequence of a 1072 nucleotide rat beta-casein cDNA insertion in the hybrid plasmid pC beta 23 has been determined. Primer extension was employed to determine the sequence of an additional 82 5'-terminal nucleotides in beta-casein mRNA. Rat beta-casein mRNA consists of a 696 nucleotide coding region, flanked by 52 nucleotide 5' and 406 nucleotide 3' noncoding regions, including a 40 nucleotide poly(A) tail. The derived 216 amino acid sequence of rat beta-casein was compared to the previously determined sequences of beta-caseins from several other species. Approximately 38% of the amino acids have been conserved among the rat, ovine, bovine and human sequences and these conserved amino acids occurred in clusters throughout the protein. One such cluster containing the majority of the potential casein phosphorylation sites was located near the amino terminus. Contrary to the considerable divergence observed for the processed beta-casein, 14 of 15 amino acids in the signal peptide sequence of the precasein were identical between the rat and ovine caseins.

Purification and properties of a major casein component of rat milk

A casein component (C2-casein) was purified by ion-exchange and gel filtration chromatography from rat milk, and the properties of this protein were examined. The molecular weight of C2-casein, as determined by Sepharose 4B gel filtration in 6 M guanidine hydrochloride, was 34 000 +/- 1000. The average hydrophobicity calculated from the amino acid composition showed that C2-casein is a rather hydrophilic protein. The alpha-helix content obtained from optical rotatory dispersion experiments was about 12%. In ultracentrifugation analyses, monomer and polymer peaks of C2-casein were both seen, and the monomer-to-polymer ratio was not affected by changing temperature conditions. C2-casein was precipitated by the presence of 2.5 mM CaCl2, and the precipitability was greatly decreased by the dephosphorylation of the protein. C2-casein was stabilized from Ca2+-dependent precipitation by the addition of another rat casein component (C3-casein) or of bovine kappa-casein.

Isolation of catfish proinsulin messenger RNA and synthesis of its complementary DNA

The purpose of these experiments was to obtain proinsulin mRNA from catfish pancreatic islets and synthesize its cDNA. Poly(A)-rich mRNA was electrophoresed on preparative agarose-urea gels. One RNA fraction was obtained which translated predominantly preproinsulin. This mRNA was estimated to be approx. 210 000 Mr (650 nucleotides) when electrophoresed under denaturing conditions. [3H]Proinsulin cDNA was hybridized to excess RNA to monitor purification of mRNA from total islet RNA. Greater than 94% of proinsulin messenger contained poly(A) sequences. [3H]Proinsulin cDNA hybridized to its template mRNA with a Rot 1/2 of 4.4 x 10(-3) mole x sec/l. The overall purification was 80-fold by this type of analysis. Thermal denaturation studies indicated a high degree of fidelity of hybrid formation between [3H]proinsulin cDNA and proinsulin mRNA. Proinsulin comprised 20% of total islet protein when synthesis was measured in vivo (Albert and Permutt, 1979) and 12-20% when total islet mRNA was translated in a cell-free system. Using the [3H]proinsulin cDNA probe it was estimated that proinsulin mRNA accounted for approx. 15% of total islet mRNA.

In vitro transcription and translation of simian rotavirus SA11 gene products

Rotavirus gene products were examined, with the simian rotavirus SA11 as a model. The endogenous viral RNA-dependent RNA polymerase associated with single-shelled virus particles or with activated double-shelled particles was used to synthesize viral RNA transcripts. Sedimentation velocity sucrose gradient analysis of the RNA transcripts revealed four peaks at 9S, 12S, 14S, and 18S, whereas agarose gel electrophoresis under partially denaturing conditions revealed eight groups of RNA species ranging in molecular weight from 2 x 10(5) to 1.2 x 10(6). The transcripts synthesized in vitro were active in an mRNA-dependent cell-free translation system derived from rabbit reticulocytes. The transcripts directed the synthesis of 11 polypeptides that had molecular weights ranging from 125,000 to 20,000 when analyzed by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. The products of in vitro translation were compared with polypeptides from purified virus and those synthesized in infected cells. Several of the polypeptides synthesized in vitro were designated as structural polypeptides by comparing the molecular weights determined by polyacrylamide gel electrophoresis analysis or by precipitation with hyperimmune serum prepared against purified virus. Three of the viral structural polypeptides (VP4, -5, and -5a) were not synthesized in vitro as primary gene products, demonstrating that processing must occur for the production of some structural polypeptides. Other in vitro-synthesized polypeptides were tentatively identified as either precursors to the viral glycoproteins or nonstructural polypeptides.

Isolation and preliminary characterization of epithelial-specific messenger ribonucleic acids and their products during embryonic tooth development

Experiments were designed to identify and characterize tissue-specific proteins involved in the process of tooth organogenesis. Epithelial and mesenchymal proteins were extracted from intact molar organs or mechanically separated tissues obtained from 25-day New Zealand White rabbit embryos. Labelling experiments with [35S]methionine followed by radioautography or gel electrophoresis and fluorography showed the presence of label only in epithelial proteins. Most of these proteins range from 43 000 mol.wt. and higher, except for one band of approx. 16 000 mol.wt. A mRNA fraction of 16--26S was isolated by ultracentrifugation on sucrose gradients. When translated in a reticulocyte-lysate cell-free system, the mRNA obtained from intact molar organs resulted in the synthesis of three proteins, of mol.wts. 65 000, 58 000 and 43 000. A similar mRNA fraction obtained from dental-pulp mesenchyme gave only the 43 000-mol.wt. protein, indicating that the 65 000- and 58 000-mol.wt. proteins are derived from epithelial cells.

Biosynthesis and secretion of milk proteins: a review

Recent years have seen a great increase in the knowledge and understanding of milk proteins. Arising from several origins including the blood stream and various cellular sources, many of the proteins found in milk are products of the secretory cells directly involved in the synthesis and secretion processes of various milk components. The lactation-specific proteins present in major amounts are synthesized in the rough endoplasmic reticulum (RER) under genetic control and undergo further post-translational modifications in their secretory route from the RER through the Golgi apparatus and secretory vesicles before ejection into the lumen with other milk components. Various molecular aspects of these mechanisms and their control are now understood, but many remain to be described.

Study of the precursors of ovine lactoproteins: primary structures of the 'signals' and enzymic processing of prelactoproteins by mammary microsomal membranes

The radiolabelled primary translation products of ovine mammary mRNAs synthesized in a wheat germ cell-free system were isolated by immunoprecipitation and analysed by automated Edman degradation. The 3 'Ca-sensitive' caseins (alpha S1, alpha S2 and beta), kappa-casein, beta-lactoglobulin and alpha-lactalbumin were found to be synthesized as precursors with amino terminal extensions of 15, 21, 18 and 19 amino acid residues respectively. The extra pieces of these various lactoproteins are similar to 'signal' peptides of other secretory proteins in their length and hydrophobicity. The occurrence of an alanyl residue at the C-termini of the extra pieces of the 6 ovine prelactoproteins suggests that the mammary proteinase responsible for the cleavage of the signal peptides may have an elastase-like specificity. When mammary mRNAs were translated in a wheat germ cell-free system in the presence of mammary microsomal membranes, pre-beta-casein was converted into authentic beta-casein as demonstrated by amino terminal sequence analyses. Additionally, pre-beta-casein was post-translationally converted into authentic beta-casein by a specific proteinase(s) extracted from rough microsomes with Na deoxycholate.

RNA synthesis in isolated nuclei of lactating mammary cells in presence of unmodified and mercury-labeled CTP

Isolated nuclei of lactating mouse mammary gland were capable of supporting DNA-dependent RNA synthesis in vitro in presence of unmodified and mercurated CTP (Hg-CTP) at high ionic condition at 25 degrees C. In presence of unmodified CTP, [3H]UMP incorporation into RNA increased linearly upto 180 min. The kinetic pattern of the reaction and the rate of RNA synthesis were essentially similar when CTP was replaced by Hg-CTP. Both in unmodified and Hg-CTP containing reactions, 70-80% of RNA synthesis was inhibited by alpha-amanitin. Presence of poly(A) in a small portion of the in vitro synthesized messenger-like RNA was detectable by oligo(dT) cellulose chromatography. Both poly(A)+ and poly(A)- RNAs sedimented with a clear peak around 15S region in a formamide-sucrose denaturing gradient. The Hg-RNA after separation from endogenous nuclear RNA by SH-agarose affinity column chromatography also sedimented around 15S region in a formamide-sucrose gradient. The Hg-RNA synthesized in the isolated mammary cell nuclei in vitro should now permit monitoring hormonal regulation of specific gene (casein) transcription in the mammary cells by molecular hybridization of the Hg-RNA with cDNA to casein mRNA.