Molecular cloning and sequence analysis of cDNA coding for canine gastrin.

We have isolated and sequenced cDNA clones encoding for preprogastrin from a canine antral cDNA library. Comparison of this sequence with those of porcine, human, and rat gastrin reveals extensive (83%) homology in the gastrin coding region as well as short regions of conserved nucleotides in the noncoding regions. The canine sequence encodes a preprogastrin of 104 amino acids which consists of a signal peptide, a 37-amino acid prosegment, and a 34-amino acid gastrin sequence, followed by a glycine (the amide donor), and flanked by pairs of arginine residues.

Interaction of (+/-)-7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene with relaxed circular pBR322 DNA.

The interaction of (+/-)-BPDE (1) with DNA at neutral pH was investigated by the application of relaxed circular pBR322 DNA. (+/-)-BPDE causes a rapid positive supercoiling of this DNA followed by a slower spontaneous relaxation. The results indicate that there are two clearly discernible types of chemical interactions between 1 and DNA, a rapid intercalative covalent binding and a slower strand breakage. The implications of these findings are discussed.

Purification and properties of the Hpa I methylase.

The purification and catalytic properties of the homogeneous Hpa I methylase is described. The enzyme exists as a single polypeptide chain with a molecular weight of 37,000 +/- 2,000 was shown by sedimentation equilibrium and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The Hpa I methylase transfers methyl groups of S-adenosylmethionine to adenine present in the recognition sequence d(G-T-T-A-A*-C), A* is the N6 methyl adenosine. An average of 2.1 methyl groups per recognition site are transferred by the Hpa I methylase.

Interaction of the HpaI endonuclease with synthetic oligonucleotides.

To determine which functional groups of bases within the grooves of double-helical DNA interact with the HpaI endonuclease, we have employed chemically synthesized octanucleotides containing base analogues. The 5-methyl group of thymine was probed as a contact between the HpaI endonuclease and its recognition sequence by using the oligonucleotides d(G-G-T-T-A-A-C-C), d(G-G-T-U-A-A-C-C), and d(G-G-T-U(Br)-A-A-C-C). The 2-amino group of guanine was probed as a contact for the HpaI endonuclease by using the octanucleotide d(G-I-T-T-A-A-C-C). The HpaI endonuclease cleaves octanucleotides d(G-G-T-T-A-A-C-C) and d(G-G-T-B-A-A-C-C) according to Michaelis-Menten kinetics. However, both the Km and turnover number for d(G-G-T-B-A-A-C-C) were severalfold lower than those for cleavage of d(G-G-T-T-A-A-C-C). In addition, d(G-G-T-U-A-A-C-C) was not cleaved by HpaI endonuclease, suggesting that the 5-methyl group of thymine is a contact between the HpaI endonuclease and its recognition sequence. d(G-I-T-T-A-A-C-C) was not cleaved by the HpaI endonuclease which may be due in part to the low thermal stability of the duplex. Nevertheless, our results suggest that the 2-amino group of guanine is a contact for the HpaI endonuclease. A phosphate group 5' external to the HpaI recognition sequence has been identified as a contact between the HpaI endonuclease and DNA. The HpaI endonuclease cleaved 5'-phosphorylated octanucleotide 30-fold faster than unphosphorylated octanucleotide. In addition, the Km of the d(G-G-T-T-A-A-C-C) was 8000-fold higher than the Km of the phage f1 RFI DNA, suggesting that the octanucleotide is too short to take advantage of the entire DNA binding site of the enzyme.

Molecular cloning and nucleotide sequence of full-length of cDNA coding for porcine gastrin.

We have cloned in EScherichia coli a cDNA copy of mRNA coding for the porcine antral mucosal hormone preprogastrin. Full-length double-stranded cDNA was synthesized and inserted into the Pst I endonuclease site in plasmid pBR322 by using a homopolymeric extension technique. A partial cDNA clone was used as a probe to identify a complete cDNA clone in a cDNA library by colony hybridization. Four positive clones were isolated, one of which corresponded to porcine preprogastrin mRNA. The nucleotide sequence of the cDNA insert (602 nucleotides) revealed 312 nucleotides in the entire mRNA coding region, 61 nucleotides in the 5' untranslated region, 86 nucleotides in the 3'untranslated region, and a poly(A) tail of 86 nucleotides. Gastrin is located near the carboxyl end of preprogastrin and is flanked at both its amino and carboxyl ends by a pair of basic amino acid residues. The presence of glycine and a pair of basic amino acid residues adjacent in the carboxyl-terminal phenylalanine of gastrin indicates that the glycine and a pair of basic amino acid residues may be required for the enzymatic amidation of phenylalanine to phenylalanine amide.

A general method for detection and characterization of an mRNA using an oligonucleotide probe.

A general method for the detection and characterization of an mRNA using an oligodeoxynucleotide probe is described. The results presented indicate that a G-dT or a dG-U base pair within a short DNA-RNA hybrid does not significantly reduce the stability of the hybrid. On this basis, we propose that 11 amino acids, including Trp and Met, can be used in selecting a peptide sequence suitable for use in designing an oligodeoxynucleotide probe complementary to a given mRNA. To test this hypothesis, we have synthesized an oligodeoxynucleotide (oligo II) complementary to the region of gastrin mRNA coding for Trp-Met-Asp-Phe and have compared its effectiveness as a hybridization probe and as a primer for the synthesis of gastrin-specific cDNA with another oligonucleotide (oligo I) complementary to the region of gastrin mRNA coding for Trp-Met-Glu-Glu. Unlike oligo I, oligo II functions as a primer in specific cDNA synthesis only when the mRNA is denatured prior to initiation of synthesis. Similarly, oligo II can be used as a specific hybridization probe for gastrin mRNA only when the RNA is denatured and partially cleaved with NaOH before hybridization. A simple procedure for denaturing gastrin mRNA to ensure efficient interaction with oligodeoxynucleotide probes is described. This procedure should be useful in studies with other oligonucleotides and mRNAs as well.

Cleavage of single strand oligonucleotides and bacteriophage phi X174 DNA by Msp I endonuclease.

Type II restriction endonucleases cleave duplex DNA at nucleotide sequences displaying 2-fold symmetry. Our data show that Msp I cleaves single strand oligonucleotides, d(G-A-A-C-C-G-G-A-G-A) and d(T-C-T-C-C-G-G-T-T) at 4 degrees, 25 degrees, and 37 degrees C reaction temperatures. The rate of cleavage of d(G-A-A-C-C-G-G-A-G-A) is several-fold faster than that of d(T-C-T-C-C-G-G-T-T). Single strand phi X174 DNA is also, cleaved by Msp I endonuclease giving well defined fragments. 5'-Nucleotide analysis of the fragments generated from single strand and replicating form DNA suggest that cleavage occurs at the recognition sequence d(C-C-G-G). The data show that Msp I endonuclease cleaves single strand oligonucleotides and prefers a recognition sequence surrounded by purine nucleotides. A general model for endonuclease cleavage of single strand and duplex DNA is presented.

Formation of biologically active peptides.

Many small biologicaly active peptides are derived from larger precursor forms which fulfil a variety of roles in the synthesis, segregation and intracellular migration of secretory products. Limited proteolysis may occur at several stages during this process, giving rise to products that are either degraded (e.g. the prepeptides) or discharged coordinately from their cells of origin during exocytosis (e.g. insulin and C-peptide). Molecular defects have recently been found to occur at cleavage sites in proinsulin as well as in other proproteins, and these point mutations may, in some instances, be responsible for familial metabolic disorders. The nature and cell specificity of the proteolytic enzymes involved in the conversion of the various precursor forms remains unresolved. Recent studies in our laboratory have led to the identification of precursors of glucagon and somatostatin in rat islets of Langerhans. Analysis of tryptic maps of these precursors has shown that a trypsin-like enzyme would be sufficient to cleave the C-terminally located somatostatin sequence from its precursor (relative molecular mass 12,500), but that both trypsin-like and carboxypeptidase B-like enzymes would be necessary to cleave the internal glucagon sequence from its prohormone (relative molecular mass 18,000). Molecular cloning techniques have provided valuable new approaches to analysing the structures of a variety of precursor forms, including those for insulin, gastrin, growth hormone, adrenocorticotropic hormone and the endorphins, and in the future will undoubtedly shed more light on the structures of their chromosomal genes, the mechanisms regulating their expression, and their evolutionary origins.

Isolation and characterization of two proteins possessing Hpa II methylase activity.

Two proteins exhibiting Hpa II methylase activity have been purified to homogeneity from Haemophilus parainfluenzae and their physical and catalytic properties have been studied. Separation of the two Hpa II methylase activities was achieved by DEAE-Sephadex A-50 chromatography. In subsequent steps, each methylase was purified separately by chromatography on Sephacryl S-200, phosphocellulose, and hydroxylapatite. The proteins have molecular weights of 38,500 +/- 1,000 (Hpa II) and 41,500 +/- 1,000 (Hpa II') as judged by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Sedimentation equilibrium analyses of the native proteins yield molecular weights of 38,800 +/- 3,000 and 42,200 +/- 3,000 for Hpa II and Hpa II', respectively, indicating that both enzymes are composed of a single subunit. Furthermore, both methylases exhibit identical specificity in the methylation of the nucleotide sequence dC-C-G-G in simian virus 40 (SV40) DNA and in a short synthetic oligonucleotide duplex. Although pH, temperature, and salt optima are the same for both enzymes, homogeneous Hpa II' methylase is more stable than Hpa II methylase. Preliminary peptide mapping indicates that the two enzymes are structurally related, suggesting the possibility that Hpa II' methylase may represent a precursor form of Hpa II methylase.

Construction and selection of recombinant plasmids containing full-length complementary DNAs corresponding to rat insulins I and II.

We have used a synthetic deoxydecanucleotide to generate an insulin-specific cDNA probe suitable for selecting transformants that contain nearly full-length cDNAs corresponding to the mRNAs coding for rat insulins I and II. Double-stranded cDNA was synthesized from x-ray-induced rat insulinoma poly(A)-RNA, inserted in pBR322 plasmid DNA by the homopolymeric tailing technique, and cloned in Escherichia coli chi 1776. Colony hybridization with oligonucleotide-primed cDNA yielded 16 positive clones of which 7 corresponded to rat insulin I mRNA and 9 to rat insulin II mRNA. Restriction endonuclease maps of representative clones of each group indicated that these contained the complete coding sequences, as was confirmed by nucleotide sequence analysis of the 5' region of the cloned DNA for rat insulin II. Nucleotide sequence analysis also established the amino acid sequence of the prepeptide of rat preproinsulin II. Comparison of the amino acid sequence of the prepeptides of rat preproinsulin I and II shows that three conservative amino acid substitutions have occurred in this region of the molecule.

Detection of gastrin-specific mRNA using oligodeoxynucleotide probes of defined sequence.

Three oligodeoxynucleotides have been chemically synthesized and used as hybridization probes to detect gastrin-specific mRNA within an heterogeneous population of RNA molecules. Using these oligonucleotides whose nucleotide sequences were deduced from the amino acid sequence of the hormone, 0.2 fmol of gastrin mRNA can be detected/microgram of poly(A)-RNA from hog antrums. The 32P-labeled oligonucleotides hybridize specifically to RNA covalently coupled to DBM-paper (Alwine, J.C., Kemp, D.J., and Stark, G.R. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 5350-5354). Labeled oligonucleotides also hybridize specifically to RNA separated by gel electrophoresis in the presence of CH3HgOH and covalently coupled to DBM-paper. Using this procedure, we have found that the mRNA coding for gastrin contains about 620 nucleotides, which is in agreement with results obtained using gastrin cDNA to determine mRNA size.

Synthesis and enzymatic properties of deoxyribooligonucleotides containing methyl and phenylphosphonate linkages.

Chemical methods for the synthesis of short deoxyribooligonucleotides containing methyl and phenylphosphonodiester linkages have been developed. The interaction of two such nonionic dinucleotide analogs, T(pCH3)T and T(pC6H5)T, with several enzymes has been investigated. Because of the phosphonate linkage each dinucleotide exists as a diastereomeric pair as shown by thin layer chromatography and enzymatic studies. Both isomers of each dinucleotide can be phosphorylated by T4-polynucleotide kinase in the presence of [gamma-32P]ATP. Only one of the diastereoisomers of each dinucleotide is slowly hydrolyzed by snake venom phosphodiesterase and acts as an inhibitor of the enzyme-catalyzed hydrolysis of 5'-labeled oligothymidylic acid. Both isomers of each dinucleotide analog are completely resistant to hydrolysis by spleen phosphodiesterase.

Detection and partial sequence analysis of gastrin mRNA by using an oligodeoxynucleotide probe.

We have used a specific deoxyoligonucleotide probe to detect gastrin mRNA in poly(A)-enriched RNA preparations from hog antrum. The nucleotide sequence of the oligonucleotide, d(C-T-C-C-T-C-C-A-T-C-C-A), was deduced from the unique amino acid sequence Trp-Met-Glu-Glu of gastrin. When used with hog antral RNA, the dodecanucleotide is an effective primer for the synthesis of gastrin-specific cDNA as judged by nucleotide sequence analysis of cDNA isolated by polyacrylamide gel electrophoresis. We have determined an 81-nucleotide sequence corresponding to the region of the gastrin mRNA that codes for the known amino acid sequence of the G34 progastrin intermediate species, and we have demonstrated the presence of two consecutive basic residues preceding the G34 sequence in the prohormone. Hybridization of gastrin cDNA or synthetic dodecanucleotide to hog antral RNA separated by gel electrophoresis on agarose gels in the presence of methylmercuric hydroxide indicates that the mRNA coding for gastrin is about 620 nucleotides long. These results suggest that the gastrin precursor peptide contains 110-140 amino acids. This method should be of general application for detection and characterization of mRNAs corresponding to proteins of known amino acid sequence.

Chemical synthesis of a self-complementary octanucleotide, dG-G-T-T-A-A-C-C by a modified triester method.

The synthesis of a self-complementary octanucleotide, d(G-G-T-T-A-A-C-C-), using a modified triester approach is described. The protected dinucleotides, d(Me2O)TribG(C1C6H4) ibG, d(Me2O)TrT(ClC6H4)T, d(Me2O)TrbzA(ClC6H4)bzA, and d(Me2O)TranC(ClC6H4)anC were synthesized by a one step triester procedure. After removal of the trityl group, the dinucleotides, dT(ClC6H4)T and danC (ClC6H4)anC were coupled to d(Me2O)TribG(ClC6H4)ibG and d(Me2O)TrbzA(ClC6H4)bzA, respectively to yield the respective tetranucleotides. The tetranucleotide, d(Me2O)TrbzA(ClC6H4)bzA(ClC6H4) and (ClC6H4)anC was detritylated and then coupled with d(Me2O)TribG(ClC6H4)ibG(ClC6H4)T(Cl6H4)T to give octanucleotide. The fully protected octanucleotide was deblocked by treatment with aqueous NH3 followed by acid and was characterized by nucleotide sequence analysis.