Special Article

Processing of Pre-mRNA in Polytene Nuclei of Chironomus tentans Salivary Gland Cells

LARS WIESLANDER,* GÖRAN BAURÉN,*⁺ KERSTIN BERNHOLM,* WEI-QIN JIANG,⁺ AND INGELA WETTERBERG*⁺
*Department of Radiobiology, Stockholm University, S-106 91 Stockholm, Sweden;
and ⁺Department of Cell and Molecular Biology, The Medical Nobel Institute, Karolinska Institutet S-171 77 Stockholm

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Abstract
Salivary gland polytene cells in the dipteran Chironomus tentans provide exceptional experimental possibilities to analyze processing of specific pre-mRNAs in intact eukaryotic cell nuclei. Here we give a brief account of how these experimental advantages can be exploited to analyze the splicing process in vivo. In multi-intron pre-mRNAs, spliceosomes assemble and splicing is initiated cotranscriptionally for all introns. Intron excision may, however, occur mainly cotranscriptionally or mainly posttranscriptionally depending on the position of each intron in relation to the remaining transcription time and intron-specific efficiencies of excision. As measured for the U2 snRNP and an SR protein, 10-15% of the spliceosomal components are bound to pre-mRNA at active gene loci at a given moment, while the majority of the spliceosomal components are present in the nucleoplasm. A continuous redistribution of the spliceosomal components takes place in the nucleus as a result of a close coupling between transcription and spliceosomal assembly.

EXPERIMENTAL CELL RESEARCH 229
240 - 246 (1996)
ARTICLE NO. 0366
Copyright © 1996 Academic Press, Inc.