Showing papers by "Michael R. Green published in 1985"

An RNA processing activity that debranches RNA lariats

Abstract: The excised introns of pre-messenger RNA's (pre-mRNA's) and intron-containing splicing intermediates are in a lariat configuration in which the 5' end of the intron is covalently joined by a 2',5'-phosphodiester bond to a specific adenosine residue near the 3' end of the intron. A 2',5'-phosphodiesterase activity in HeLa cell extracts has been detected that debranches RNA lariats, converting them to linear RNA molecules by specific cleavage of the 2',5'-phosphodiester bond. This lariat debranching activity is distinct from previously reported 2',5'-phosphodiesterases with regard to its biochemical and substrate requirements as well as its stringent cleavage specificity. The debranching activity is observed only if the RNA lariats generated during in vitro processing are deproteinized and added back to the extract. These results suggest that during the normal in vitro splicing reaction the 2',5'-phosphodiester bond of RNA lariats is protected from cleavage by the lariat debranching activity.

Role of the 3′ splice site consensus sequence in mammalian pre-mRNA splicing

Abstract: Pre-mRNA splicing has been shown to occur by a two-step pathway. In the first stage, the pre-mRNA is cleaved at the 5' splice site, generating the first exon RNA species and an RNA species composed of the intron and second exon (IVS1-exon 2 RNA species). In the second stage, cleavage at the 3' splice site and ligation of the exons occurs, resulting in the excision of the intact intron. The excised intron and IVS1-exon 2 RNA species are in the form of a lariat in which the 5' end of the intron is joined to an adenosine residue near the 3' end of the intron by a 2'-5' phosphodiester bond. Here we show that although cleavage at the 3' splice site does not occur until the second stage of the splicing reaction, at least a portion of the 3' splice site consensus sequence is necessary for 5' splice site cleavage and lariat formation. Thus, in higher eukaryotes at least three sequence elements participate in the initiation of the splicing reaction: the 5' splice site, 3' splice site consensus sequence and the RNA branchpoint.

4'Epidoxorubicin (epirubicin): activity in hepatocellular carcinoma.

Abstract: Doxorubicin provides the most consistent response rate in hepatocellular carcinoma. We therefore initiated a trial with its analog 4'epidoxorubicin. Eighteen patients, all without prior treatment, were given the drug as a single agent every 3 weeks with dose escalation whenever possible. Five patients were treated by six-hour infusion and 13 by intravenous (IV) bolus injection, with the median dose being 90 mg/m2. The patients were of diverse ethnic background and included some with underlying cirrhosis and hepatitis B surface antigenemia. Three patients had partial remissions (6, 12, 48 weeks) for a response rate of 17%. Four patients also had prolonged stable disease (14, 26, 27, 38 weeks). Toxicity was mild, although cardiac toxicity developed in three patients at 685, 825, and 1,460 mg/m2 cumulative dose. The response to 4'epidoxorubicin in this study appears to be equivalent to the reported response rates for doxorubicin, with decreased toxicity.

Synthesis of Hybridization Probes and RNA Substrates with SP6 RNA Polymerase

Abstract: Single-stranded RNA molecules of defined sequence are useful as substrates for the investigation of such cellular processes as RNA processing and translation, and when highly labeled they serve as extremely efficient hybridization probes. An in vitro transcription system based on the unusual properties of SP6 RNA polymerase facilitates the synthesis of homogeneous single-stranded RNA molecules of any desired sequence. In this chapter we describe the SP6 transcription reaction in detail and point out the advantages and disadvantages of the use of single-stranded RNA molecules as substrates and as hybridization probes. In addition, we review recent studies on the use of SP6 transcripts as anti-sense RNAs that can hybridize to mRNAs in vivo and thereby block translation of a particular gene product.