RESUMO
Nuclear poly(A)+ RNA was isolated from gastrula and early tadpole stages ofXenopus laevis, transcribed into cDNA and integrated as double stranded cDNA by the G-C joining method into the Pst cleavage site of plasmid pBR 322. After cloning inE. coli strain HB 101 the clone libraries were hybridized to32P labelled cDNA derived from nuclear poly(A)+ RNA of the two different developmental stages. About 20% of the clones gave a positive hybridization signal thus representing RNA molecules of high and medium abundance. From these clones, some individual clones were identified containing sequences which are not present at the oocyte and gastrula stages but which are transcribed at the early tadpole stage of embryonic development.
RESUMO
Nuclear poly(A)+ and polysomal poly(A)+ RNA were isolated from gastrula and early tadpole stages of the amphibianXenopus laevis. Complementary DNA was synthesized from all RNA preparations. Hybridization reactions revealed that at least all abundant and probably most of the less frequent nuclear and polysomal poly(A)+ RNA species present at the gastrula stage are also present at the early tadpole stage. On the other hand, there are nuclear RNA sequences at the latter stage which appear, if at all, only at lower concentrations at the gastrula stage. The polysomal poly(A)+ RNA hybridization reactions suggest the existence of polysomal poly(A)+ RNA sequences at early tadpole stages which are not present in the corresponding gastrula stage RNA.By cDNA hybridization with poly(A)- RNA it could be shown that most of the poly(A)+ containing RNA sequences transcribed into cDNA were also present within the poly(A)- RNA. It was estimated, that these sequences are 10 fold more abundant within the poly(A)- polysomal RNA and 3-6 more abundant within the poly(A)- nuclear RNA as compared to the poly(A)+ RNAs.