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U7 Small Nuclear RNA in C Snurposomes of the Xenopus Germinal Vesicle

Chung-Hsiun Herbert Wu and Joseph G. Gall
Proceedings of the National Academy of Sciences of the United States of America
Vol. 90, No. 13 (Jul. 1, 1993), pp. 6257-6259
Stable URL: http://www.jstor.org/stable/2362370
Page Count: 3
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U7 Small Nuclear RNA in C Snurposomes of the Xenopus Germinal Vesicle
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Abstract

In the amphibian germinal vesicle small nuclear RNAs (snRNAs) occur in morphologically distinct structures called snurposomes. Three types (A, B, and C) have been distinguished on the basis of cytological appearance and snRNA composition. C snurposomes in Xenopus are spherical bodies ranging in diameter from <1 μ m to about 10 μ m. They stain intensely with antibodies against trimethylguanosine and the small nuclear ribonucleoprotein-specific Sm antigen but give weak or negative in situ hybridization reactions for the snRNAs involved in pre-mRNA splicing (U1, U2, U4, U5, and U6). We show here that C snurposomes in the Xenopus germinal vesicle contain U7 snRNA, an snRNA of low abundance involved in processing the 3' end of histone pre-mRNA. Xenopus U7 is 58 nucleotides long and is capped at the 5' end with trimethylguanosine. C snurposomes are often associated with B snurposomes, which contain the splicing snRNAs but not U7; B and C snurposomes together constitute a morphologically complex structure known as a sphere or sphere organelle. Although most spheres and C snurposomes are extrachromosomal, a few are attached at the histone gene loci on chromosomes 8, 9, and 16. Because they contain U7 snRNA and occur at the sites of histone pre-mRNA synthesis, C snurposomes presumably play a role in processing histone transcripts.

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