Gene-specific silencing by expression of parallel complementary RNA in Escherichia coli

Gene-specific silencing refers to a phenomenon in which expression of an individual gene can be specifically repressed by different mechanisms on the levels of transcription, RNA splicing, transport, degradation in nuclei or cytoplasm, or blocking of translation. In different species gene-specific silencing was observed by expression or injections of antiparallel double-stranded RNA formed by a fragment of mRNA and antisense RNA. Here we show a potent and specific gene silencing in bacteria by expression of RNA, that is complementary in a parallel orientation to Escherichia coli lon mRNA. Moreover, the expression of parallel RNA is more effective at producing interference than expression of antisense RNA corresponding to the same mRNA region. Both effects of interference mediated either by parallel RNA or antiparallel RNA gradually decrease up to the 40th generation. Together with in vitro nuclease protection studies these results indicate that a parallel RNA duplex might be formed in vivo and both types of duplexes, antiparallel or parallel, can induce gene-specific silencing by similar mechanisms.

Reverse transcription, amplification and sequencing of poliovirus RNA by Taq DNA polymerase

A model for virion RNA of the poliomyelitis virus, which does not pass the stage of DNA copies during biogenesis, demonstrates that Taq DNA polymerase is capable of synthesizing 960-bp cDNA with the specific primer. When comparing the nucleotide sequence of the starting virion RNA and recombinant DNAs, isolated from several independent clones, copying and amplification of virion RNA appear accurate (one substitution per 960 bp). A comparison of Taq and Tth DNA polymerases in RT/PCR indicates that the sensitivity of Taq polymerase seems to be two orders of magnitude higher than that of Tth polymerase. The RNA detection level under the chosen conditions approached 10(4) RNA copies per test. The present investigation indicates the great versatility of Taq polymerase, which promoted the reverse transcription reaction of RNA, cDNA amplification, screening of recombinant clones as well as sequencing of recombinant DNA. Thus application of Taq polymerase is rather promising not only to detect nucleic acids in biological samples, but also for isolating and cloning individual genes, encoded on DNA and/or on RNA templates.

Regulation of intracellular proteolysis in Escherichia coli cells by antisense mRNAs of the lon gene

To explore the possibility of regulating proteolytic processes in Escherichia coli cells, a series of plasmids directing the synthesis of antisense mRNAs complementary to different regions of the lon gene was constructed. The effect of these antisense mRNAs on the rate of degradation of abnormal proteins (14C-labelled polypeptides containing puromycin or canavanine) in the bacterial cells was studied. The greatest inhibitory effect occurred in the case of a mRNA complementary to the regulatory region at the 5' end of the lon gene. The reasons for the differences in the efficiency of lon gene antisense mRNAs in inhibiting proteolysis are considered.