trans

C H A P T E R
3
Transcription
Arthur Günzl
University of Connecticut Health Center,
Farmington, CT, USA
INTRODUCTION
Mechanisms of transcription have been analyzed
in great detail in a few model organisms
such as the budding yeast Saccharomyces
cerevisiae, mouse and human. In contrast, our
knowledge of the transcription machinery and
the mechanisms of transcriptional regulation
in parasites is rather limited. There is one
notable exception: Acanthamoeba castellani, a
facultative parasite causing keratitis and acute
encephalitis in humans, has been an excellent
subject for transcriptional studies and, in particular,
RNA polymerase (pol) I-mediated transcription
has been meticulously investigated
in this organism. Details of this work can be
found in several excellent reviews by M.R. Paule.
In most other parasites, the lack of suitable
assay systems has prevented the investigation of
transcriptional processes. However, DNA transfection
has now been established for several
important parasites, and in vitro transcription
systems have been developed for trypanosomatid
and nematode species. This technology has
enabled structural analysis of gene promoters.
Moreover, specific promoter element/protein
complexes have been identified, and a few
proteins of the transcription machinery characterized.
Thus far, the most detailed knowledge
has been obtained in trypanosomatid species
and, therefore, they are a focus in this chapter.
The general picture
The details of eukaryotic transcription are
described in numerous books and reviews.
Nevertheless, the following brief overview
should be helpful to understand parasitespecific
aspects of transcription presented in
the remainder of the chapter.
Whereas prokaryotes have a single DNAdependent
RNA polymerase, eukaryotic organisms
harbor three such enzymes in the nucleus,
each serving a distinct function in RNA synthesis.
RNA pol I transcribes exclusively the
large ribosomal (r)RNA gene unit (rDNA), RNA
pol II synthesizes mRNA plus several small
RNAs, e.g. the U1–U5 small nuclear (sn)RNAs,
Molecular Medical Parasitology
ISBN 0–12–473346–8
47
Copyright © 2003 Elsevier Science Ltd.
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