Genetics in an oocyte

The combination of DNA cloning in bacterial plasmids and DNA injection into frog oocyte nuclei permits a novel type of genetic analysis in which the function of defined sequences of DNA may be more readily and precisely investigated than before. Purified segments of chromosomal DNA containing 5S genes of Xenopus have been injected into the nuclei of Xenopus oocytes and the products of these genes recognized as labelled 5S RNA. Since short linear molecules of DNA are degraded in oocytes, the function of particular regions of DNA near a 5S gene is best determined by excising these regions and joining them to other kinds of DNA. This is achieved most simply by inserting regions of 5S DNA into a plasmid. Our results with alpha-amanitin show that the activity of a 5S DNA promoter inserted into a plasmid can be detected independently of the plasmid's own promoters, using DNA injection into oocytes. The observation that plasmids containing variant 5S genes result in the synthesis of abnormal 5S RNA molecules illustrates the possibility of mutanting recombinant plasmids and then testing the biological effect of these mutations by DNA injection.