Expression of ribosomal insertion in Drosophila: sensitivity to intercalating drugs.

Ribosomal insertions in Drosophila are transcribed at very low levels. The abundance of the most prominent 0.8 kb type 1 insertion transcript increased up to 60-fold when cultured cells were exposed to the DNA intercalating drug chloroquine. After injection of insertion-containing rDNA in circular form into Xenopus laevis oocytes an apparently identical 0.8 kb insertion transcript was synthesized, and its accumulation was stimulated several fold by coinjection of chloroquine or ethidium bromide. We suggest that ribosomal insertions are assembled in a chromatin conformation that lacks unconstrained torsional stress, accounting for the inactivity of these DNA regions; introduction of stress by intercalation results in activation of transcription from the insertion sequences

Three new members of the RNP protein family in Xenopus.

Many RNP proteins contain one or more copies of the RNA recognition motif (RRM) and are thought to be involved in cellular RNA metabolism. We have previously characterized in Xenopus a nervous system specific gene, nrp1, that is more similar to the hnRNP A/B proteins than to other known proteins (K. Richter, P. J. Good, and I. B. Dawid (1990), New Biol. 2, 556-565). PCR amplification with degenerate primers was used to identify additional cDNAs encoding two RRMs in Xenopus. Three previously uncharacterized genes were identified. Two genes encode hnRNP A/B proteins with two RRMs and a glycine-rich domain. One of these is the Xenopus homolog of the human A2/B1 gene; the other, named hnRNP A3, is similar to both the A1 and A2 hnRNP genes. The Xenopus hnRNP A1, A2 and A3 genes are expressed throughout development and in all adult tissues. Multiple protein isoforms for the hnRNP A2 gene are predicted that differ by the insertion of short peptide sequences in the glycine-rich domain. The third newly isolated gene, named xrp1, encodes a protein that is related by sequence to the nrp1 protein but is expressed ubiquitously. Despite the similarity to nuclear RNP proteins, both the nrp1 and xrp1 proteins are localized to the cytoplasm in the Xenopus oocyte. The xrp1 gene may have a function in all cells that is similar to that executed by nrp1 specifically within the nervous system

Mossbauer spectroscopy of synthetic and naturally occurring staurolite

Room temperature Mossbauer spectroscopic measurements of 23 natural and 12 synthetic staurolite samples, the latter representing both Fe-Mg and Fe-Li solutions, demonstrate that the majority of the Fe in all samples is Fe2+ which occupies the Fe1, Fe2, and Fe3 subsites of the tetrahedral Fe site in an average ratio of 43/12/27. Mossbauer parameters of the various sites do not vary systematically with composition and appear to be independent of next nearest neighbor effects (except in the case of H). These results corroborate previous structure refinement data on the existence of three major Fe subsites and provide direct evidence of minor Fe occupancy in the octahedral sites. -from Author