Mercurated nucleotides: assessment of a new tool to study RNA synthesis and processing in isolated nuclei

Enzymatic polymerization of 5-mercuriuridine-5'-diphosphate with polynucleotide phosphorylase from E. coli

We report the polymerization of 5-mercuriuridine-5'-diphosphate (ppUHgX), in the presence of an excess of beta-mercaptoethanol, with polynucleotide phosphorylase from E. coli. A degradation of mercurated nucleotides with mercaptans was observed and about 30% of incorporation of mercury in the polymer was obtained after treatment with pancreatic RNase. The influence of ppUHgX and pUHgX with or without beta-mercaptoethanol was also studied on the polymerization of UDP. The ppUHgX did not polymerize in the absence of beta-mercaptoethanol.

Separation of mercury substituted RNA synthesized in isolated rat liver nuclei

The population of RNA molecules synthesized in isolated rat liver nuclei in vitro in the presence of [3H]CTP and Hg-UTP was successfully fractionated into at least two subfractions containing various proportions of mercury label. Fractionation was achieved either by step-wise chromatography of Hg-RNA on thiopropyl-Sepharose columns or by density gradient centrifugation in metrizamide. The fraction of RNA heavily labeled with Hg-UTP was composed mainly of 4--18S RNA and contained virtually all radioactivity derived from [gamma-32P]ATP or [gamma-32P]GTP. The slightly mercurated RNA fraction consisted mainly of longer RNA molecules (12- greater than 28S) and was not labeled with [gamma-32P]ATP or [gamma-32P]GTP. Labeling with gamma-32P nucleoside triphosphates was sensitive both to rifamycin AF/013 and heparin whereas labeling with [3H]CTP was fully resistant to the inhibitors and showed sensitivity to low doses of alpha-amanitin. We assume that the observed subpopulation of heavily mercurated RNAs consists of RNA molecules initiated in vitro.

Simian virus 40 transcriptional complexes incorporate mercurated nucleotides into RNA in vitro

Simian virus 40 Sarkosyl transcriptional complexes incorporated mercurated nucleotide precursors into preinitiated RNA chains. Synthesis with mercurated precursors was three- to fivefold slower than with nonmercurated nucleotides (12 to 20 pmol per 10(6) cells per h at 25 degrees C), and 50 to 70% of the RNA product bound specifically to sulfhydryl-agarose. The amount of mercurated CMP incorporated into RNA was measured by specific binding of [35S]cysteine to the mercury residues. More than 90% of the mercurated RNA hybridized to simian virus 40 DNA.

Transcription of Friend virus proviral sequences in isolated nuclei

Transcription studies using isolated Friend nuclei and Escherichia coli polymerase are presented. Combination of the techniques of thiol-Sepharose chromatography and cDNA-Sepharose hybridisation has resulted in a system in which the transcription of the Friend virus proviral sequences with endogenous and E. coli polymerase can be examined. The results show that the percentage of Friend viral-specific sequences in RNA transcribed by E. coli RNA polymerase and by endogenous RNA polymerase in isolated nuclei are similar. The percentage of viral-specific sequences synthesized in isolated nuclei is similar to that found in Friend cell nuclear RNA.

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.

The reactions of mercurated pyrimidine nucleotides with thiols and with hydrogen sulfide

In the presence of thiols, 5-mercuripyrimidine nucleotides are quantitatively converted to 5-thiomercuri derivatives, but these compounds are unstable and decompose at a rate dependent on the nature of the thiol. The decomposition involves three different reactions and proceeds via a symmetrical mercury derivative of the nucleotide. The end product is the unmodified nucleotide. Similar reactions occur in the presence of hydrogen sulfide. Since mercurated nucleoside triphosphates are substrates for RNA- and DNA polymerase only in the form of thiomercuri derivatives, this implies that when DNA is replicated or transcribed in vitro with a mercurated substrate, the latter is rapidly demercurated to the unmodified substrate which is incorporated as well. Hence the product of the in vitro synthesis can only be partially mercurated in any one pyrimidine. Also, formation of cross-links in the resulting polymer is possible.

In vitro RNA synthesis and expression of vitellogenin gene in isolated chicken liver nuclei

Optimal conditions for prolonged in vitro synthesis of RNA in isolated chicken liver nuclei have been described. It is shown by incorporation of gamma32P-GTP into RNA, analysis of the product on sucrose density gradient, and digestion with alkaline phosphatase and ribonuclease A that there is reinitiation of RNA synthesis. Polynucleotide kinase activity has been ruled out as explanation for the incorporation of gamma32P-GTP. alpha-Amanitin inhibits RNA synthesis by about 50%. Nuclei prepared from estradiol-treated chicks have twice the RNA synthesis activity as the controls. RNA is synthesized in the presence of Hg-UTP and the mercurated product separated by affinity chromatography on sulfhydryl-Sepharose column under stringent conditions. Vitellogenin mRNA sequences are measured by hybridization with DNA complementary to vitellogenin mRNA. Estradiol treatment leads to a 10-fold increase in vitellogenin mRNA sequences.

Mapping of adenovirus late promoters with nascent mercurated RNA

Nascent RNA molecules were labeled in vivo and elongated in vitro by incubation of the isolated nuclei in the presence of mercurated nucleotides. The RNA molecules initiated and labeled in vivo and elongated in vitro were then selectively purified on a thiopropyl 6-B Sepharose affinity column. The procedure was shown to be free of artifacts since the addition of mercurated nucleotides and the retention on the affinity column is mediated by the endogenous RNA polymerase II (nucleoside triphosphate:RNA nucleotidyltransferase; EC 2.7.7.6), is sensitive to actinomycin D, and is dependent on the presence of all four ribonucleotide triphosphates. This general procedure was applied to the mapping of viral promoters late after adenovirus 2 infection of HeLa cells. RNA purified as described above was hybridized to restriction enzyme fragments attached to nitrocellulose filters. The 5' ends of the nascent RNA chains are located in coordinates 9.5-17 for a rightward transcript, 0-25 for a leftward transcript, and possibly 60-70 for a second rightward transcript. These locations clearly differ from locations of the early promoters and therefore suggest that the transition from early to late functions is controlled at the transcriptional level.