Ribozyme transcribed

In most cases, the DNA inserted into the MCS for expression is not a genomic gene with the original exon/intron configuration, but a cDNA. In exceptional cases, antisense RNA or ribozymes may be expressed. cDNA lacks intronic sequences, but still has the 5 and 3 UTR sequences. As discussed above, the presence of the 3 UTR may reduce the stability of mRNA transcribed from the cDNA insert. Furthermore, the length and secondary structure of the 5 UTR may influence the efficiency of translation. Therefore, it is generally recommended to use cDNA with only short 5 and 3 UTR sequences for expression with expression vectors. 

Ferre-D Amare, A. R., and Doudna, J. A. (1996). Use of cis- and trans-ribozymes to remove S and S heterogeneities from milligrams of in vitro transcribed RNA. Nucleic Acids Res. 24, 977-978. 

The preparation of twin ribozymes included both chemical and enzymatic procedures. Basically, in our laboratory RNA strands longer than 60 nucleotides are transcribed from synthetic DNA templates using T7 RNA-polymerase. By using 5-benzylmercapto-lH-tetrazole [18a,b] as activator in the phosphoramidite approach, however, we also succeeded in synthesizing a chemical version of HP-... 

Advanced virology. RNA viruses and retrotransposons predated the formation of DNA vimses in the pre-cellular virus world of Koonin et al [18]. Precellular ribosome-like entities might have been operated by ribozymes and RNPs. Cellular ribosomes could remain operational extracellularly (Heinrich Matthaei and Marshall Nirenberg, vide infra). In the cellular world, there are two enzymes that transcribe RNA to DNA telomerase and reverse transcriptase (RT). The gene of the enzyme RT is a component of the retroviral genome [32]. Template-encoded proteins of this complexity are not expected to have been formed in the pre-cellular era, unless precellular RNP-armed entities resembling ribosomes existed. 

Ribozymes Appeared. Tetrahymena thermophila revealed its group I intron ribozymes in Thomas Czeh s laboratory. Ribozymes catalyze their substrates ( like protein enzymes ) infra- and intermolecularly. The tetrahymena ribozyme s intramolecular catalysis consists of self-splicing (Golden BL et al Howard Hughes Medical Institute, Department of Chemistry and Biochemisby, University of Colorado, Boulder, CO. Science 1998 282 259-264). Alu ribonucleoproteins consists of polymerase Ill-transcribed Alu sequences and signal recognition proteins (SRP9/14) united. In the ribosome, these units inhibit IRES-mediated (internal ribosome enfry site) translation initiation (Ivanova E et al Nucleic Acids Res 2015 43 2874-2887). 

For RNA, artificial self-cleaving hammerhead ribozymes with a triazole linkage at the active site are reported [26]. Interestingly, triazole backbone modifications in RNA by CuAAC and SPAAC chemical hgation of 3 -azide and 5 -cyclooctyne oligonucleotides can further be reverse transcribed into DNA while one nucleotide is omitted at the linkage [95]. 

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