Transcription fraction TFIIIC can regulate differential Xenopus 5S RNA gene transcription in vitro.

Abstract

An extract of whole oocytes (oocyte S150) differentially transcribes Xenopus oocyte and somatic 5S RNA genes. In the oocyte S150, transcription complexes with different stabilities are assembled onto oocyte and somatic 5S DNA. The stability of the transcription complex is dependent on activities present in a fraction containing transcription factor TFIIIC. This fraction stabilizes the binding of the positive transcription factor TFIIIA to a somatic 5S RNA gene much more efficiently than it does to an oocyte gene. The oocyte S150 transcription extract is deficient in TFIIIC such that supplementation with a fraction enriched in this transcription factor selectively stimulates oocyte 5S DNA transcription. Previously it has been shown that an egg extract deficient in TFIIIA selectively transcribes somatic 5S RNA genes. Thus under conditions where there is differential stability of transcription complexes, limitation of either TFIIIA or TFIIIC may exaggerate the differential expression of two genes.

Two TFIIIA activities regulate expression of the Xenopus 5S RNA gene families.

“…Although different forms of TFIIIA present during oo genesis and early embryogenesis have not been observed previously, our data are not inconsistent with the con clusions of previous studies (Wolffe and Brown 1987;Wolffe 1988). We beheve that both the relative abun dance of the two forms of TFIIIA and the absolute con centration of other transcription factors are critical for active expression of the oocyte-type genes.…”

“…Recently, we Peck et al 1987) and others (McConkey and Bogenhagen 1987;Wolffe 1988;Xing and Worcel 1989) have been able to repro duce the preferential transcription of somatic-type genes in vitro with extracts prepared from mature oocytes or eggs (Glikin et al 1984). These results were not depen dent on transcription reaction conditions, DNA concen tration effects, or differential RNA stability.…”

“…In this regard, Millstein et al (1987) have shown that stable inactive complexes are formed on the oocyte-type genes in S-150 extracts and that these complexes are refractory to acti vation after microinjection into living oocyte nuclei; however, Wolffe (1988) has shown that the addition of a crude protein fraction containing TFIIIC and other pro teins to S-150 extracts can elevate oocyte-type transcrip tion. Thus, evidence for both explanations is currently available.…”

“…Thus, evidence for both explanations is currently available. Wolffe andBrown (1987, 1988) proposed that the inactivation of oocyte-type transcription observed during early embryogenesis is due to destabilization of transcription complexes formed on oocyte-type, but not on somatic-type, genes. The biochemical mechanism re sponsible for this destabilization has yet to be estab lished.…”

Role of maturation-promoting factor (p34cdc2-cyclin B) in differential expression of the Xenopus oocyte and somatic-type 5S RNA genes.

“…Whole oocyte S-150 extracts exhibit a 50:1 to 100:1 S:O preference (28,29,33). This is due to the limitation of TFIIIC in these extracts (48) and to the lower affinity of oocyte-type genes than of somatic-type genes for this factor (22,23). When oocytes mature in vivo or when cultured oocytes are induced to mature in vitro by incubation with progesterone, oocyte chromatin condenses and the oocyte nucleus (the germinal vesicle) breaks down.…”