ANA POMBO AND PETER R. COOK
CRC Nuclear Structure and Function Research Group, Sir William
Dunn School of Pathology, University of Oxford, South Parks Road,
Oxford OX1 3RE, United Kingdom
Abstract
Sites of transcription in the HeLa nucleus are not diffusely
spread throughout euchromatin but are concentrated in ~2000
discrete sites or "transcription factories." These sites can be
immunolabeled after allowing permeabilized cells to elongate
nascent RNA chains in the presence of BrUTP. Splicing factors are
also concentrated in a few tens of nuclear domains known as
"speckles"; they are also more diffusely spread throughout
euchromatin. As there has been some controversy whether the
speckles are sites of transcription, we investigated the relative
distributions of transcription factories and the speckles
(detected using Sm autoimmune antibodies). We used conditions
that minimize the redistribution of both the nascent RNA and the
antigens during permeabilization and fixation and imaged the
sites with high resolution using cryosections and a "confocal"
microscope. The speckles continued little--if any--nascent RNA
and so were usually not transcriptionally active, but they were
often surrounded by a few transcription sites. Whether they are
active sites of processing of RNA or merely sites where the
machinery is stored remains to be established.
EXPERIMENTALL CELL RESEARCH 229
201 - 203 (1996)
ARTICLE NO. 0360
Copyright © 1996 Academic Press, Inc.
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