Transcriptional characteristics of in vitro assembled chromatin assayed by microinjection into <i>Xenopus laevis</i> oocytes

DNA sequencing and subsequent functional in vitro analysis of the Xenopus laevis rDNA transcription termination has led to the identification of three transcription termination sequence elements: T1, located at the 3' end of the 28S rDNA; T2, a putative processing site 235 bp downstream of T1; T3, the principal terminator positioned 215 bp upstream of the gene promoter. As demonstrated for nuclear run-off assays, T3 was found to be the main terminator for Xenopus rDNA transcription. These in vitro data are in obvious contradiction to results obtained by electron microscopic (EM) spread preparations from rapidly isolated amplified oocyte nucleoli, i.e., an rDNA chromatin probe thought to represent the in vivo situation, indicative of transcription termination at sites T1-2. However, most interestingly, T3 had--again by the EM method--been identified as the exclusive terminator for NTS spacer transcription units. In order to answer the question of whether read-through transcription of the complete rDNA spacer sequence is obligatory for 40S pre-rRNA in vivo transcription, we analyzed several hundreds of spread rRNA genes from Xenopus oocyte nucleoli in great detail, applying two different spreading procedures, e.g., dispersal of amplified oocyte nucleoli shortly in detergent-free or detergent containing low-salt media prior to the EM spreading technique. Quantitation of EM spreads resulted in the finding that read-through rDNA spacer transcription beyond T1-2 termination sites (i.e., indicative of T3 transcription termination) can be visualized for the in vivo situation at a frequency of less than 3% of rRNA genes analyzed.(ABSTRACT TRUNCATED AT 250 WORDS)

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Faithful in vivo transcription termination of Xenopus laevis rDNA

Meissner

Hofmann

Steinbeißer

et al. 1991

Chromosoma

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Expression of cloned genes and translation of messenger RNA in microinjected Xenopus oocytes

Heikkila¹

1990

International Journal of Biochemistry

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Transcriptional characteristics of in vitro assembled chromatin assayed by microinjection into Xenopus laevis oocytes

Cited by 2 publications

References 14 publications

Faithful in vivo transcription termination of Xenopus laevis rDNA

Faithful in vivo transcription termination of Xenopus laevis rDNA

Expression of cloned genes and translation of messenger RNA in microinjected Xenopus oocytes

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