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Transcription and Processing of Nematode tRNA Genes Microinjected into the Frog Oocyte

Riccardo Cortese, Douglas Melton, Theresa Tranquilla, John D. Smith


With the development of cloning techniques, large amounts of pure segments of DNA, which may include pure single genes, can be obtained and their nucleotide sequences determined. The purified segments can be used to obtain general information on the organization of the genes in the total genome and also to study gene expression. To this end, in vitro systems have been successfully employed for eukaryotic genes (Birkenmeier et al. 1978; Schmidt et al. 1978; Ng et al. 1979). An alternative in vivo system based on the special properties of the frog oocyte has been developed by Gurdon and his colleagues (Mertz and Gurdon 1977; Brown and Gurdon 1977, 1978; Gurdon et al. 1979). The oocyte is large enough to allow purified DNA segments to be injected directly into its nucleus. This system has the advantage that one may reasonably expect that all the transcription and processing components will be intact. Here we present a summary of our results on cloned tRNA genes of the nematode Caenorhabditis elegans and their expression in Xenopus laevis oocytes.

The tRNA genes are particularly suitable for studies aimed at correlating structure with function because the tRNAs themselves are easily characterized. They constitute a group of genes of related function that are expressed coordinately in many physiological conditions. On the other hand, the expression of some tRNA genes is subject to an individual mode of regulation, particularly evident in some extreme cases, such as in the silk gland of Bombyx mori (Garel et al. 1970) where...

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